R 22

Rhodes 22


12 Volt Charging

With respect to charging requirements for a Group 27 battery that typically is rated at about 95-amp hours, a 5 watt unregulated solar panel as listed in West Marine puts out a maximum of 0.3amps at 14v in full sun.

To recharge a partially discharged battery that was say 1/3 discharged or 30amp hours would require at least 100 hours of full sunlight. These things are good to maintain a full charge on a battery that is only lightly used. Nav lights typically pull about 1-1/4 to 2 amps total so it would take 4 to 6 hours of sun time to recharge from an hour's use of running lights. I think the panels GB uses are 15 watts. A solar charger will not recharge a completely discharged battery, nor will the charger built into most outboards. My Evinrude 6hp has a 3-amp charger. To recharge that same 30 amps would require at least 10 hours of run time at 2500 rpm or faster. I haven't run the motor for 10 hours total time all summer!

If the battery is discharged more than 75%, a charger that puts out 15 to 20% of the battery's rating is needed to fully restore the battery to its capacity. This is because a higher charge current is needed to initiate the chemical process that converts the lead sulfate on the plates back into lead and sulfuric acid. So a 95-amp hour battery should be charged at about a 15-amp to 20-amp rate initially.

With a typical 2 or 3 stage regulated charger the current will drop as the battery reaches about 80% of capacity until the unit is trickle charging at typically 2 amps. So the last 20% of charge will require about 8-10 hours. So total charge time will be typically be around 18 to 20 hours or so with this size of charger for a fully discharged battery.

You can roughly check charge state of the battery with a DC voltmeter. A fully charged battery just off the charger will read around 13.2 volts. After a couple of hours off the charger it should stabilize around 12.9 volts. Anything less than 12.8 volts is not a full charge. A fully discharged but undamaged battery will read around 10.5 volts. 50% discharge is generally around 12.2 volts. For longest battery life batteries should be regularly recharged to at least 85% of capacity or about 12.7 volts and maintained there and not discharged below 50% in normal use.

This information applies to standard wet cell batteries. Gel cells generally need a different charging regimen and special chargers to prevent damage from overcharging. If you overcharge a wet cell battery it just boils off water from the electrolyte that can be replaced.

Sitting in a discharged state for long periods of time causes the lead sulfate to flake off the plates, permanently reducing capacity. Also extended periods without charging allows the sulfuric acid to separate from the water and settle to the bottom of the case, also reducing capacity, this is called stratification. The last 20% of the charge cycle is very important for protecting against stratification as the gas bubbles generated at this stage provide agitation to remix the acid and water. This is where solar chargers are really handy to prevent premature battery death.


Measure the voltage of your batteries with a DC voltmeter. Typically a full charge is 13.2 to 13.6 volts, half charge is around 12.3-12.5 volts, and fully discharged is 10.5 volts. Anything below 10.5 and the battery is history. Measure it after the battery has been off the charger for a couple of hours so it has a chance to stabilize.

If they are near full discharge they need to be charged at a minimum 10-amps per hour rate for 6 to 8 hours if they are group 27 size. This will bring them to about an 80 percent charge level. They then need to be trickle-charged at a 1 to 2-amp rate for an additional 24 hours to equalize and restore full charge to all cells.

Let them cool for a couple of hours, top them off with distilled water if they need it, and recheck voltage. If it is not fully charged then there are probably weak cells from the plates sulfating. You may get some additional use from them if your loads are not too high but they won't last much longer and the capacity is reduced.

A typical 15 to 20 watt solar panel or 1 amp trickle charger will take around 80 hours at full output to recharge a fully discharged group 27 battery in good condition. If the battery has been in a partially discharged state for a long period of time it requires a high amperage charge rate rather than the solar panel or trickle charger.


A quick question or questions on electrical-maybe naive-but is there been a better wetcell battery on the market than others? I used the Seavolt (WM house brand), mostly for daysailing and some nighttime. I only got 3- 1/2 years with trickle charge over the winter and a start this season at 14+ volts.

My solar got disconnected, the battery discharged and now won't take a charge at all. It also seems my electrical system is not grounded and the alternator didn't help. Any link on cell care and feeding or general review?

23 May 2001

What are you using to charge the battery? Once a battery is pushed extremely low, it takes a high voltage charger to bring it back. A trickle charger will not work and your boats alternator is most likely too weak also. When you run them dead like that it does take a lot of life out them, but you might be able to recharge it and get another season out of it.

You might be able to take it into a car garage and see if they can charge it. Be sure to top off with distilled water first.

23 May 2001

add only distilled water to a used lead acid battery (was acid poured out).

23 May 2001

Using a Sears 10 amp/2 amp Autocharger. There are no readings off specific gravity at any cell, but I'll top off the cells and try more than overnight. This is a straight deep cycle and I've been lucky before to get 6 years typical out the Seavolt in the past. Thanks.


PS. Any suggestions on where and how to check the grounding of the electrical system on a 1997 R22? Bi-data meter hasn't worked or alternator charging since...

23 May 2001

The only thing I know about boat alternators is that it is best to attach them to the battery with locking nuts. The typical wing nuts that come with a lot batteries tend to come loose, and the loose connection ruins something in the charging system.

Your 10 amp charger might not be strong enough, but I don't think it hurts anything to try.

Maybe someone on the list would know if thick jumper cables attached to your tow vehicle would work. You only need the extra juice to get things started. Once the battery is charged a little with the high volt system, you can switch to your regular charger for the rest.

23 May 2001

The electrical system on a boat is not grounded as it is on a car. There are two lines for every circuit, between each device and the source. The source may be a buss or the battery. The two lines are +12 vdc and 0 vdc. Switches or other control elements are in the +12 vdc line. You need to test for circuit continuity using a multmeter which reads both dc volts and resistance (ohms).

Check voltage at the battery and use as a reference. Then check various locations to determine if power is available when it should be. Any appreciable drop from battery voltage indicated a high resistance connection in the circuit, most likely caused by corrosion. No voltage indicates an open circuit. Repair as needed, using the ohmmeter to check for continuity.

Locate where the alternator leads are connected to your system. It may be at the battery, the buss, or at the battery switch. With the motor off you should read battery voltage. Start the motor and promptly check the voltage at that point. It should be at least 13.6-14 vdc. If there is no increase in voltage with the motor running your alternator is not charging. It may be defective wiring, but most likely, you have blown diode(s) in the alternator.

Shut motor off. Disconnect charging wires at boat connection point. Use the multimeter (resistance setting, lowest scale) to check the continuity of both wires between the boat connection point and the motor connection point. Should read "0" ohms (or extremely close). If OK, the alternator needs service. If not, check and clean wiring and plug.

The diodes can be tested on the motor but uless you really know what you are doing you may do more harm than good.. Some diodes are clip in units and easily removed. Note polarity if you remove them and be sure to replace with same polarity or you may cause serious damage. Either take diodes or motor (as case may be) to an electrical shop, have tested and repaired.

Hope this helps.

23 May 2001

A link with a lot of info: http://www.windsun.com/Batteries/Battery_FAQ.htm

I know nothing, good or bad, about this company.

23 May 2001

One should never add acid to a lead acid battery, only distilled water. Specific gravity is an indication of state of charge. The chemical reaction that generates power oxidizes the positive grid lead plates into lead sulfate and reduces the acid to water resulting in a lower specific gravity. Charging the battery reverses this reaction, breaking down the lead sulfate back into sulfuric acid and lead. Unlike nickel cadmium batteries, led acid batteries do not have memory.

The usual cause of short life is excessive discharge and inadequate charging. If the battery is in good condition one will have to replace about 115% of the amp hours consumed to bring the battery up to full charge. Most boat batteries are left in a partially discharged state for long periods of time which results in the lead sulfate changing to a crystalline form that is very hard to break down.

A trickle charger or solar panel will not fully charge a deeply discharged battery. The battery must be bulk charged to 80% of capacity at a current rating of 30% to 40% of the amp hour rating. For a typical Group 27 battery rated around 85 amp hours this means a charge current of at least 25 to 30 amps for 3 hours followed by low amperage 2-3 amps for 10 to 20 hours to reach full charge. Full charge is indicated by a specific gravity of between 1.275 and 1.3 or a measured voltage of at least 12.8 volts.

If the battery is left in a discharged state for long periods, the remaining acid may sink to the bottom of the case leaving only water in contact with the grid plates, making the battery very difficult to recharge as it is highly resistive and looks like a fully charged battery to the charger. Such a battery may show a high charge voltage but not be able to deliver any current and will show a low specific gravity. Adding acid won't help and creates a serious danger of explosion as charging will produce large amounts of hydrogen gas from electrolysis of water.

If you use a small automotive type 2 stage battery charger that can't deliver more than 10 amps, it can take several days of charging for the lead sulfate crystals to break down to the point that the battery will accept a full charge. During this time you will see the charge current start off high, then drop to a low rate, typically around two amps.

If you pull the inspection covers and the electrolyte is not bubbling, then the battery is no where near a full charge, it is just too resistive from sulfation and low specific gravity to accept a charge. If you leave the charger on for a day or so, you will see the electrolyte begin to bubble as water is converted into hydrogen and oxygen gases. This is good as the bubbles agitate and remix the electrolyte and also help to mechanically break down the lead sulfate crystals.

The battery may consume a fair amount of water in this process. Just make sure there is plenty of ventilation so there is no danger of hydrogen buildup. At some point if the battery is recoverable, the charge current will start to rise again. Make sure to keep the battery topped off with distilled water. Once a day stop charging and let the battery cool for a couple of hours. Check the voltage after it has cooled. It should read around 13.2 volts. Let it sit for 24 hours. The voltage will drop to around 12.9. If it drops below 12.8 the battery is still not fully charged or has lost some of its capacity. Or ideally check the specific gravity at a room temperature of 70 degrees. It should be between 1.275 and 1.3 for a full charge, or all the little balls should float.

As I write this my 70AH group 24 battery which was left on the boat over the winter is on its second 24 hour charge cycle using a common 6 amp 2 stage automotive type charger. The first 24 hours brought it up to about 12.5 volts, roughly a 70% of capacity charge. A battery which cannot maintain this voltage over a 24 hour period with no load is near the end of its useful life.

24 May 2001

If the battery is only used for motor starting, then you should be okay for the season. Lead acid batteries do self discharge over time if they just sit though. The motor will easily replace the drain of starting in most cases, but won't fully recharge a deeply discharged battery if other loads are on it. You can periodically check it with a volt meter, 12.8-13.2 volts is considered a full charge. 12.2volts is about 50% discharged, 10. 5volts is fully discharged. If it drops below 50% I would pull it and recharge it on a shore charger.

A solar cell would maintain it at a fully charged state, but will not fully recharge a deeply discharged battery. The solar cells are good because they prevent sulfation build up by keeping the battery at or near a fully charged state. Partially discharged batteries that are not fully recharged from time to time will build up hardened lead sulfate deposits that will eventually kill the battery.

19 Apr 2001

Get your recording of military bugle calls out and play taps. Then go to your nearest "Interstate" battery outlet and plunk down the necessary dollars to replace your battery. Average life with tender loving care should be around four to five years. I just replaced mine, 185 amp hours for around $80.00.

23 May 2001

We had left our batteries aboard during a cross country move and they were very low this spring when I got around to working on the boat. Running our charger at the normal settings did not phase the batteries.

Our charger has settings for deep cycle, regular and "start". The start position offers high amperage to allow starting a car engine. It also forces a high amperage charge into a reluctant battery. While the battery actually read something like 13.5 volts, it had no juice. I put the charger on manual charge, and start position and let it charge for a couple of dasys. Since I have two batteries in parallel, I was effectively pushing around 7 amps into each battery.

It takes quite a bit of current to ovecome that really weak battery. Rafe is right that maybe a service station charger will get some life out of your battery. Two seasons ago we just about gave up on our existing batteries. But using the charger in the extreme charger position salvaged them... again. They are 5 years old and still maintaing a charge. For now.

Alex Bell
23 May 2001

I got 6 years out of my 280Z battery. That car ran so good, it was a shock when it would not start. I had never thought about the battery in that, and it was another shock when I figured out it was the original battery.

I use Interstate batteries in autos. Jeep has one. But I don't think they offer deep cycle batteries. Never checked, but never saw them either.

23 May 2001

SAomehow I never figured you for a 280X kind of a guy. Go figure. Interstate has deep cycle batteries.....very reasonably priced compared to others and they tested well against the other brands. I'm off to da boat.....gotta install the new sterso today.....don't want to work on the weekend ys know.

23 May 2001

I forget the name, but what happens is a "crud" builds up on the plates of the battery when it is discharged that no longer dissolves back in to the battery acid solution and block the plate from the solution. Also is breaks off and falls to the bottom shorting out the plates. Bad news all around. It only needs to sit like that for a few weeks to be history. The deep cycles are built with heavy plates and a change in the lead alloy to hand this better and can be brought back with a "equalization" charge. But "starting" type batteries just die. I think you have a starting battery. Get a true deep cycle this time not one of those half/half's. I like the lifeline AGM deep cycle .

23 May 2001

Here's the Interstate website. There is a link to "Marine/RV" further down that page is a link to technical specifications. They list two deep-cycle Group 24s and two Group 27s.


Notwithstanding, I got about 5 years from my Sears DieHard.

23 May 2001

Check to make certain the battery has no dead cells. Be sure it has plenty of fluid in it. Batteries have memory. You may need to connect a light or some small appliance to it and run it all the way down.... You can purchase a specific gravity checker for the fluid for a very small investment. You may need to add some acid. Once the fluid is at the right specific gravity it should take a charge....Follow manufacturer precautions on the charger and the battery to avoid catastrophic accidents...! ! !........

23 May 2001

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