Hi Everyone, 

I run a small battery (THIS ONE) to power a 7in Helix and some interior LED lights. This year, I added a 9in Helix to the bow, which I have been running off the same battery. However, now that battery can only last me about 5 hours before the Helix units drain it down. Since space is very limited on my boat, and I don't want to get rid of the old battery for a bigger one, am I able to purchase a second one and wire in parallel? 

 

I wasn't sure if I can wire my on-board charger to charge the two batteries in parallel

I wasn't sure if the increased amps is okay for the two units, I didn't want to mess something up!

 

Will this work okay, or is it better to scrap the battery and try to squeeze a larger battery in there for my electronics (space is tight)

 

 

You can rig a second one in parallel, but it's best to buy the two together.  You'll only have as much capacity as the weaker battery allows.  

 If you connect rechargeable batteries in parallel and one is discharged while the others are charged – the charged batteries will attempt to charge the discharged battery. With no resistance to slow this charging process, the charged units can overheat as they rapidly drain and the discharged battery can overheat as it attempts to charge at well above its design capabilities.

Borrowed

I'm not an expert on batteries & battery chargers, however I've hung around experts on this subject, from time to time and from what I remember it is pretty important to have both of your batteries be the same age-wise.  Assuming your batteries are the same to start, wiring batteries in parallel will roughly double your run time.   Running the two depth finders of batteries in parallel will extend your running time somewhat - the will tell how much - probably depends alot on how much your them.

I wouldn't  charge the batteries while they were wired in parallel - don't know enough about batteries to say exactly why it wouldn't be good, but I don't think it would.   Why not just buy a 2 bank charger?   Then you will know, with very little doubt, that the two batteries are being charged the same.

I bought a 2 bank charger at the beginning of the season for my cranking and electronics batteries, hoping to not waste that money and swap into a 3 bank charger   I'm starting to think I will just be tossing this battery and upgrading to a larger one, not pleased, but this battery is one year old and has probably about 50 cycles on it, so I'm not too confident in buying another to run in parallel