Powerboat leisure battery question

[flip805]

Hi I have a Leader 805 which has 3 (same make, in parallel ) x 125ah leisure batteries, one has failed completely the other 2 are holding good charge. Is it ok to replace it with another manufacturers 125ah battery or do they all need to be matched? 

many thanks from a newbie :-) 

Phil

[Capt’n Ron]

Hi Flip805, unfortunately, you should replace all 3 batteries at the same time, even if 1 or more are still holding a charge. The reason is they should be balanced so they charge and discharge evenly, which makes them more efficient. 

I use Pacific Yacht Systems as a reference. Jeff has a lot of information on batteries and electrical so you should take a look at their site. 
Pacific Yacht System


Cheers,
Ron

[Charlie-Bravo]

Ron is giving good advice, if you replace just one battery the new one seems to get dragged down to the level of the older.

You could remove the dodgy one and just link the remaining two , it may give you enough capacity for your needs depending on how power hungry you are, and what you need. ......... but somebody has thought that 3 batteries was a good idea in the past.
Replacing one can be done, similar chemistry capacity and construction ,  and is cheaper ....... but cheaper in the short term, sooner or later you will need a new set , 3 good new batteries will last you for many years and is just another running cost of boat ownership.

CB

[flip805]

Many thanks for the advice Ron and CB

I'll look into replacing all 3 :-) 

[Capt’n Ron]

A couple more things to consider before you replace your batteries.  Batteries and electrical take a bit of math calculations to determine how much you need and how much is usable, and what the remaining voltage actually means; 12.7v is 100% charged where as 11.9v is fully discharged.  Here is a thread to a discussion on electrical that should help “Link to electrical and batteries

Basically, if your current parallel 3 125Ah (total 375 Ah) batteries are flooded you actually only have 30% (112.5Ah) useable.  If you replaced them with 2 120Ah AGM batteries (240Ah), you actually get 55% useable from AGM, or 132Ah, and if you use Firefly batteries you can get 65% useable.  The AGM cost more and are a bit heavier, but you would have fewer batteries and have less issues than flooded.  

Take a look at the link where you will see more details.

Ron