Replacing Domestic Batteries - Problems and your thoughts.

[jac]

My boat has a wholly inadequate domestic battery - single lead acid 105 Ah. As you might expect it’s on the list to address this winter. It’s not totally straightforward as the current space for batteries is full so some surgery/ re wiring will be needed.

However …My battery is dead. As in not enough to run a chartplotter and instruments for more than an hour or so despite a lot of charging.

So I’m faced with the choice of doing it properly, spending several weekends building new battery boxes, installing batteries, new cables, resetting chargers etc to a different profile or simply dropping in say one replacement AGM now and then over the winter, finishing the job.

I’m happy to buy a pair of larger AGMs now so they would be same chemistry, size, batch etc- it’s just that one would be used a few times before it’s partner got installed.

I know the “proper” answer is to spend the time now and do it properly bu if I do that I potentially write off most of what is left of the season (especially after deducting weekends when I’m busy anyway ) - so that leaves me with a simple drop in one now, accept the different battery profiles caused by use but enjoy a couple more weekends of sailing.

So my question.

Does anyone have any practical information on how much battery longevity will be affected if I just drop one in now and then do the other one in 3-4 months time?

I should say that use over the next couple of months will probably be day sailing, maybe a weekend or two but left over the week mid river with a small solar panel to ensure fully topped up.

 

[chris-s]

So long as it is not abused then I doubt you would really notice any measurable difference.

 

[Aja]

I would think 'not much'.

 

[geem]

I know this is not what you were thinking but you could buy 8x105Ah lifepo4 cells and clamp them together to form a single bank. This would fit in your single battery box. You would then install a pair of JK bms so you run the 8 cells as two 12v (4cell) batteries. You would have 210Ah of capacity equivalent to 350Ah of lead all achieved in the space of a single 100Ah lead battery. Alternatively, just install 4 cells and a single jk bms and you would have space for the jk bms and fuse in the battery box as well.
You may not fancy going down the lithium route but for anybody else in the same situation, it is very achievable but more expensive than just dropping a new lead acid battery in as you need to add in the cost of bms, dc/dc charger and a fuse. I paid €48/cell for grade A 105Ah cells in the US last year

 

[footsoldier]

jac

I think you may have already made your mind up - go for your plan A, it makes sense.

If you are not already familiar with them, the TAYNA website offers a huge range of batteries, delivered next day at very keen prices and you can do some forward planning by closely studying their detailed dimensions, amp-hours etc.

 

[vyv_cox]

My boat had 3 x 110 leisure batteries, one for starting, two for domestic. After a couple of years I needed to increase the size of the domestic bank, which I did by combining the three and adding a Red Flash for a starter. Despite the wildly different service there seemed to be no downside to this and the bank lasted a couple more years.

 

[fredrussell]

My boat has a wholly inadequate domestic battery - single lead acid 105 Ah. As you might expect it’s on the list to address this winter. It’s not totally straightforward as the current space for batteries is full so some surgery/ re wiring will be needed…

Rather than do that why don’t you just drop a single 100 a/h LiFePo battery in instead, along with a dc to dc charger. Shazam! Same useable amount of power as two 105a/h lead acid (well, nearly) and no surgery to boat required. Have a look at what lithium batteries cost these days. You may be surprised.

 

[Buck Turgidson]

Switch everything off. Get a plastic folder for your chart and use your magnetic compass and go sailing. Fix it over the winter.