upgraded battery bank now problems

before my weekend boat outing i upgraded my battery bank from two battery system, one start/one house by buying three brand new deep cycle batteries for the house bank and one starting battery. so i have 4 batteries total. new set up ran fantastic but problem is i ran on batteries alone the entire weekend. lol seems the alternator was not charging these batteries so my voltage dropped throughout the weekend, till right when pulling out died completely, needed to use jump pack to start. any ideas?

one thing topoint out right before my battery died completly i noticed hitting trim up was drawing a ton of power, as if the boat was running off of battery power only. then one last trim adjustment boat shut off and died. battery now dead. thinking maybe alternator wasn big enough for 3 batteries i eliminated everything but one battery (these are brand new 27 series) , but it wont even charge one battery. boat worked fine before, did i fry an alternator somehow, or did it coincidentlly go bad? or did i hook something up wrong? they are wired parallel. please someone help... thanks alot

ps engine is a 5.7 mercruiser stern drive.

Re: upgraded battery bank now problems

Your alternator is not man enough to charge up 4 batteries, especially when draining them down past the 50% mark.To test your alternator, run the engine on the muffs and check to see the current output into the battery with a multimeter. Or take it to an auto parts store to have it bench tested.

Re: upgraded battery bank now problems

thanks fireman, had a feeling that was the problem, makes sense. but do you think i could have done damage to my altenator? before i bought these new batteries, when i was only running one battery i would see the volt gauge climb when i was underway. now idont. assuming alt is not big enought to charge all these batteries, i eliminated 2 of my 3 supply batteries to see if my boat would work as it did before since im only under one battery now. it wasn the case, the volt meter still does not move with rpm.... could the battery just be way too low to show any charge during this small sample, or could i have screwed up my alt? also what size alt would i need for 3 house batteries, one start battery>?

Re: upgraded battery bank now problems

Odds are good you took out the weak link, ie the alternator.

I've seen seemingly healthy alternators immediately smoke when trying to charge a deeply drawn down spiral wound battery. (optima) Multiple wet batteries in parallel would do the same thing. Be sure whatever alternator you use can pull full load indefinitely without damage.

Re: upgraded battery bank now problems

thanks for the advice jmartin. earlier in the day i lost footing and slipped into my engine compartment. i broke my fall on the side alt is on, turns out i pulled the wire loose .... oops. anyhow, its back and working like normal again. the alt is 55 amp, is this sufficient for 3 batteries if they are not deeply drawn? or could i potentially have problems down the road?

Re: upgraded battery bank now problems

I would isolate my batteries on a two position switch (1, 2, both, off) and use two as house batteries and 2 as cranking/reserve batteries. Your alternator shouldn't have too much trouble keeping up with that as long as you don't deplete either bank too low. You can also install an isolater, which will allow the alternator to only charge the battery that needs it.

Re: upgraded battery bank now problems

Seems to me you're asking an awful lot of a 55 amp alternator.