View Full Version : Some Battery Questions

08-05-2005, 03:06 PM
* I just picked up my first AGM battery from West Marine. I was wondering if it will harm the battery if I drain it more than 50% like it would a lead acid battery.

My battery says it has a discharge rate of 3% per month. Does this mean it loses 3% of its total amps and can never be regained, or can you recharge the 3% of power the battery discharged?

Thanks for the help!

08-05-2005, 11:51 PM
I'm not a battery expert, but I have some experience with AGM's. We use them at work in a deep cycle aplication. They seem to last a long time. I think that when they refer to 3% loss per month I believe they mean that if the battery sits unused for a month it will lose 3% of it's charge. It should recharge completly. Sometimes we store them for many months in our warehouse before using them and they seem to do fine. I assume that the battery you bought is for deep cycle use.

We buy Concorde AGM's from Advanced power products. Their website has some info that might be handy. Here is the link

Tight lines

08-06-2005, 07:49 PM
The battery loses 3% of its total charge a month. Batteries like to be charged all the time. Buy yourself a nice little trickle charger that charges about 1.5 amps to 2 amps. Whenever you don't use the boat plug it in. It won't build up a charge but it will help keep your battery in good shape.

If you really want to get fancy buy a three phase charger. The first phase basically charges like heck and builds up a charge in the battery fast. The second phase kicks in when the first phase gets the battery 80% charged. The first phase can't charge any more than that because it overheats the battery and a hot battery holds less charge. The second phase charge is smaller and slower and gets the battery up to 100%. Then the third phase kicks in, a trickle charge that maintains the battery.

Your battery will last longer and you will have more charge in it, if you get the three phase charger. You can find them for around 100 bucks. A trickle charger runs around 30 bucks.

Your battery will also last longer if you can do something to keep it from getting hard bumps. Bumping a battery breaks sulfur something deposits off of the lead plates and this causes the battery to lose capacity for a charge. Best place for a battery is rear of the boat, the smoothest ride.

The more expensive batteries do things to reenforce the lead plates so they don't leach the sulfur deposits and last longer because of it.

The worst thing you can do for a lead acid battery is not use it. Sitting around for the winter is not good for it. This is all true for your car battery, too.

08-07-2005, 08:08 AM
Let us know in two or three years how the AGM battery is working out, and if it was worth the extra $bang$ to purchase.

I second the above posts about getting a 3 phase charger. There is no sense getting an expensive battery then skimping on the charger.

08-08-2005, 11:52 AM
You won't harm the battery till you discharge it more than 80% of capacity, just be sure to charge it back up when you get home.. AGM batteries are really good and you should get many years of service out of it, as long as you don't neglect it.

08-08-2005, 05:39 PM
I just recieved two AGM batteries and a charger for my boat. I will be converting from a single battery to a dual system. Can anyone geve me any pointers befor I start? Thanks

08-09-2005, 09:26 AM
Hogs do you want them to act like one battery or two seperate batteries?

08-09-2005, 10:52 AM
I will be hooking them up as a primary and a backup. What I'm looking for is recommendations as to what size wires I should run, and how far apart can I place the batteries, and any other advice that someone may be willing to give. Thanks

08-09-2005, 11:39 AM
If you want to set them up as two seperate batteries, you can do this and still charge both of them off the motor with a Perko Switch, it lets you select which one you want to use at any given time, and I think they have one that will let you select both at one time also.

As far as wire size goes 1 guage or 1/0 guage should be fine as long as your wire runs aren't huge ( under 20')
1 guage is about the size of standard jumper cables and 1/0 is bigger.

You can place the batteries anywhere on the boat with the use of the Perko Switch, just remember that the farther away from the switch you are the bigger the wire you should use, also use STRANDED wire on D.C currant not single strand like Romex * D.C currant does not travel inside the wire like A.C it travels on the outside of the wire's, thats why all battery cables like in your car are stranded wire and not solid!! * hope this helps.. check out the link


08-09-2005, 12:35 PM
Thanks that helps. Where do you suggest I buy the wire?

08-09-2005, 12:46 PM
For your big runs buy welding cable. It is cheaper than most other wires and has great conductivity. They will have the copper crimp ends at the same store. I rewired my trailer house with it as well. No more wiring problems to the converter/charger. ;)

08-09-2005, 12:54 PM
Metal is right on the wire, welding cable is cheaper than say thnn or something thats U.L listed

08-09-2005, 01:16 PM
One more thing, coat all of your connections, including the battery terminals, with anticorrosion grease. Vaseline works really well. Thanks Doc. ;D 8) ;D

08-09-2005, 01:44 PM

Looks like your boat and goddies are awsome,, bet it's one heck of a fishing sled ;)

08-09-2005, 01:48 PM
Thanks Sun. It's my divorce/semiretirement present to myself. 8) ;D 8)

08-09-2005, 01:55 PM
Metal where do you fish at?

08-09-2005, 02:05 PM
Check P.M. ;)

08-10-2005, 08:34 PM
Welding wire is cheap but you really want tinned marine wire. It will cost you and make up for it by lasting much longer.

As for the Perko switch, it's a second best choice as you have to manually change it and if you forget your battery doesn't get charged. The better choice is to get what they call a Combiner. I believe it works with the Perko, but it automatically sees that both batteries are charged and keeps the systems seperate for discharging.

I'm not real clear on it, but I have been looking into dual charging systems for a boat that I am currently wiring.

08-11-2005, 08:46 AM
This link may help

http://www.cabelas.com/cabelas/en/templates/pod/standard-pod-wrapped.jsp?_DARGS=/cabelas/en/common/catalog/pod-link.jsp_A&_DAV=MainCatcat21276&rid=&indexId=cat60 0056&navAction=push&navCount=1&parentType=index&pa rentId=cat600056&id=0032185