battery water going low on only 1 battery

First if the battery has a CCA rating (Cold Cranking Amps) or an CA or MCA rating (Cranking amps or Marine cranking amps) it is MOST LIKELY a starting battery not a true deep cycle (Thoguh there is no reason not to computer the cranking amps for a Deep cycle, that's not their primary use so it's not common)

With batteries in paralles. if one is "Very thirsty" compared to the other, there are only two (well 2.2) possible answers
1: Bad connection, only one battery actually in use, other just taking up space
2.1 One battery failed: High resistance, Just sitting there taking up space
2.2 One battery failed, Shorted cell, sucking up water as a result.

In either case, Take 'em out, Charge them one at a time and haul to Auto store for testing.. Replace with a pair of GC-2 Six volt Golf car batteries in SERIES 230 amp hours at 12 volts, cost about the same as 150 amp hours of 12 volt type and are TRUE deep cycle.

Drat, marketing wins again.

2 of those duralast 12v marine/dual purpose batteries are More money for less capacity, compared to the Eastpenn/deka golf cart battery I linked from Batteries +





12v dual purpose battery on left, 6v golf cart battery on right:


Source:
http://www.pbase.com/mainecruising/deep_cycle_battery

For Marine batteries depth of discharge for greatest number of cycles is quite shallow. For a 100 amp-hour jar, only 20 amp-hours should be used.

Here are the specs:

Duralast battery

I like AutoZone batteries.

I see no autozone duralast battery with 845CCA, I'll stick with my guess.

Landy it is not a delco nor a duracell. It is a Duralast 845. Probably a group 29 12 volt jar.

Nope, just marketing mumbo jumbo

googling duracell 845 yields this:

https://www.batteriesplus.com/replacement/battery/ac-delco/845a/sligc115

Looks like a East Penn/Deka golf cart battery at 230AH

Genuine upgrade.

Hi,

The new ones sound as if they are either Marine or Starter batteries. These do not last well when deep cycled.

845 may be the cold cranking rate.

What is the 20 hour amp-hour rate?

I had 1 bad battery and the 2nd had a bad cell. The best battery was dated 3/15 and the other had no date. They were not matched batteries.
So much for the seller telling me that he put new batteries in.
I up graded to 2 Duralast 845 amp batteries.
These should hold for a long time.
I do have a new converter with smart load.

Thanks for the replies.

I'll let you know how they check out.