AGM Batteries, worth the extra.

[JimC]

My services battery is coming up for replacement. It's done four years which is about as much as I seem to get from any regardless of make. I used the sealed type as it does away with the need for a battery box and lets me have a slightly bigger battery, 110 a/h. My question is: is it worth stumping up for an AGM battery? I understand these have advantages in terms of lifetime and charge-retention on standing etc. Built-in charger is a Dolphin 3 stage with 14.4 volt bulk charge, stepping down 13 point something (don't have the manual here).

 

[pvb]

My question is: is it worth stumping up for an AGM battery? I understand these have advantages in terms of lifetime and charge-retention on standing etc.

Decent AGM batteries do have a longer cyclic life, but usually cost considerably more than ordinary batteries. If you only have one battery now, you'd be better spending any extra cash on a second battery, to be wired in parallel, to double your Ah capacity. For a given discharge, the batteries will have a greatly reduced depth of discharge, and this should double their cyclic life expectancy. A larger bank will also accept charge from your alternator more readily, helping to increase charging efficiency. I use ordinary maintenance free "sealed" batteries in my domestic bank with good results.

 

[vyv_cox]

I have sealed 110 Ah batteries on my boat in Greece and in UK. One set is by Bosch, the other is Numax but both types are apparently able to deliver high current for starting but accept cycling to relatively low voltages without being destroyed. Too early to tell their long term reliability yet, both sets two years old. In each case the local chandler, who I trust, says they have very good results from them.

 

[JimC]

...If you only have one battery now, you'd be better spending any extra cash on a second battery, to be wired in parallel, to double your Ah capacity. For a given discharge, the batteries will have a greatly reduced depth of discharge, and this should double their cyclic life expectancy. A larger bank will also accept charge from your alternator more readily, helping to increase charging efficiency.

Thanks for that. Sounds good. My alternator ouputs 55 amps max. Will there be any problem in charging the greatly increased capacity. I seem to remember reading somewhere that there is an optimum range for the relationship between alternator output and battery load?

 

[pvb]

Thanks for that. Sounds good. My alternator ouputs 55 amps max. Will there be any problem in charging the greatly increased capacity. I seem to remember reading somewhere that there is an optimum range for the relationship between alternator output and battery load?

No problem. I have a 90A alternator charging 660Ah of domestic batteries. Works fine.

 

[JimC]

Thanks.

 

[Otter]

50amp alternator charging 420ah domestic bank so no problem, in fact it may be kinder to your batteries and prevent possible damage by overcharging with the alternator.

 

[Contest1]

I bought a couple of second hand 110 ah agm. Very pleased with their out put and voltage reading 12.6 after charging via the alt.
The bilg pump shorted an drew both, down to almost zero, didn,t cop it the first time.
Basic altenator 35 amps couldn,t revive so boughr a 220 v 16 amp smart charger, Brought them home and both now fully charged.
I think the claims about thier recovery and reliability are genuine.

 

[GeorgeTina]

Hi
I use AGM batteries on my yacht. 180 amp/hours for domestic and 26 amp/hours for starting. Since the yacht is in Italy and wintered on the water the batteries are not charge for 5 to 6 months during the winter. After this time I am still able to start the 2GM20 on the starter battery without a charge and the domestic shows 80 to 90% charge. The batteries have lasted 8 seasons so far. I try not to discharge below 50% on the domestic but it has been down to 25% a few times. I bought AGM as I knew I would be unable to charge the batteries over the winter period and this would see off normal wet cell batteries. I have not noticed any reduction in the amp/hours available and can still last 48 hours on the hook without having the run the engine. Standard alternator 55amp and 15amp 3 stage charger, split charging via a FET splitter. So I am well pleased with the performance so far.

 

[onesea]

I have just asked similar questions on this thread, I have stated what I have bought and why over on that thread as I do not wish to hijack this thread...