Thread: Charging batteries in parallel?

I've got a 12v trolling motor that I'm going to run two batteries in parallel, or so I think. I had intended on getting a 24v system this year, but haven't. I got a 3 bank charger as a gift, but I can't hook it up to both of the trolling motor batteries can I? I'm just trying to get the most out of what I've got.

With a 3 bank you can charge both tm bats plus start bat. Just connect each bank to each Bat.

Originally Posted by wilbur

With a 3 bank you can charge both tm bats plus start bat. Just connect each bank to each Bat.

exactly right

I'll be darn, thank guys! I just figured they would be working against each other if the batteries were still hooked to each other.

If you are charging batteries wired in parallel I would advise seperating them somehow when charging them with a three bank charger. Some type of disconnect needs to be used when charging them and then reconnect them once they are charged and you are ready to use them. The charger will not be able to determine when each individual battery is fully charged if they are connected together in parallel and will eventually damage batteries and charger.

Originally Posted by Reel Man

If you are charging batteries wired in parallel I would advise seperating them somehow when charging them with a three bank charger. Some type of disconnect needs to be used when charging them and then reconnect them once they are charged and you are ready to use them. The charger will not be able to determine when each individual battery is fully charged if they are connected together in parallel and will eventually damage batteries and charger.

X2,
if your batteries are wired parallel you can simply charge them by hooking the charger up in this order using only one bank of your charger,positive lead batteryA,then negative lead batteryB;otherwise you with have to disconnect the the parallel leads in order to charge using the 3 bank charger!!!!

Originally Posted by strmwalker

X2,
if your batteries are wired parallel you can simply charge them by hooking the charger up in this order using only one bank of your charger,positive lead batteryA,then negative lead batteryB;otherwise you with have to disconnect the the parallel leads in order to charge using the 3 bank charger!!!!

Right On!

Just use both banks with the batteries in parallel. The charger uses current draw to know when the battery is charged and will shut down when they are charged.

Originally Posted by filletfetish

I'm going to run two batteries in parallel, or so I think.

Let's back up to your basic plan before solving the charger puzzle. Parallel hookups are not the best way to use your two batteries. As ReelMan points out, batteries charge and discharge at different rates--even a pair of identical batteries purchased at the same time.

It's true that hooking a pair of batteries in parallel lengthens your TM's running time but that's all you get. A two-battery parallel bank doesn't increase the TM's power. What you don't see happening (but will eventually learn from experience) is that the stronger of your two batteries will charge the weaker one. On the water, that means a bank will deliver less run time than the sum of the individual batteries.

A better plan is to hook your batteries to an A/B/Off switch. Start your day switched to the weaker of the two batteries and run it down to a safe voltage--a level that will not do permanent damage to the battery's plates, probably 12.00v. Then switch to your other (fully-charged) battery for the second half of the day. Doing it this way, you can squeeze every useable amp out of your batteries & protect them in the process.

Now, we come back to your original question. With an A/B/Off switch in place, two banks of your charger can be hooked to the batteries without concern. Should you choose an A/B/A+B/Off switch, you'll want to set the switch to any setting except A+B while you charge.

Originally Posted by Corker

Let's back up to your basic plan before solving the charger puzzle. Parallel hookups are not the best way to use your two batteries. As ReelMan points out, batteries charge and discharge at different rates--even a pair of identical batteries purchased at the same time.

It's true that hooking a pair of batteries in parallel lengthens your TM's running time but that's all you get. A two-battery parallel bank doesn't increase the TM's power. What you don't see happening (but will eventually learn from experience) is that the stronger of your two batteries will charge the weaker one. On the water, that means a bank will deliver less run time than the sum of the individual batteries.

A better plan is to hook your batteries to an A/B/Off switch. Start your day switched to the weaker of the two batteries and run it down to a safe voltage--a level that will not do permanent damage to the battery's plates, probably 12.00v. Then switch to your other (fully-charged) battery for the second half of the day. Doing it this way, you can squeeze every useable amp out of your batteries & protect them in the process.

Now, we come back to your original question. With an A/B/Off switch in place, two banks of your charger can be hooked to the batteries without concern. Should you choose an A/B/A+B/Off switch, you'll want to set the switch to any setting except A+B while you charge.

This is very good info. I had wondered if my run time would actually double or not. My initial thoughts were that I can usually make it all day on one battery. So, by adding the extra, it would be a sure bet. So, let's talk about maximizing!

I know that the extra battery can't deliver more power, but what happens when you start to lose to battery power? For instance, on days I pull cranks or when I'm facing a strong wind, I'll have to increase the speed setting to account for the draining battery as the day goes on. If it were in parallel, I would be carrying a higher voltage level over a longer period of time. Shouldn't that increase the overall run time? I've got no problem installing a switch or disconnect, or disconnecting the parallel connection. I'm just wanting the most effecient, and safe, way to this situation.