AGM bats

Unless you can't keep them more or less upright, is there any situation where AGM is worth the extra cost over a standard lead acid battery?

I'm fast coming to the conclusion that, if you need more than a flooded battery can supply, the next step is LiFePO, and we're close to the point where LiFePO is the battery of choice for anyone who does long passages or spends a a lot of time at anchor. Seems like we're fast getting to where it's worth while for anything more than hopping from marina to marina, too.
 
Stemar said:
Unless you can't keep them more or less upright, is there any situation where AGM is worth the extra cost over a standard lead acid battery?

I'm fast coming to the conclusion that, if you need more than a flooded battery can supply, the next step is LiFePO, and we're close to the point where LiFePO is the battery of choice for anyone who does long passages or spends a a lot of time at anchor. Seems like we're fast getting to where it's worth while for anything more than hopping from marina to marina, too.
Click to expand...
Definitely worth considering AGMs for 2 reasons. They do not need any different charging from lead acid and pound for pound (money) they have a longer life in terms of discharge cycles. Add to that they accept higher charge rates and have lower self discharge. Costs have come down dramatically since cars started to use them, particularly those with stop start systems. So now a nominal 100AH FLA may be £90, an automotive AG M (with approx twice the potential life) £130 and an upmarket "marine" AGM like a Lifeline £400 with again double the potential life.

FLA are fine for most light users (pretty much most of UK weekend sailors) and typically will last 5/6 years. AGMs should last 10 years (mine are already 6 years old). This of course assumes you look after them, don't discharge them too deeply and keep them as fully charged as possible when the boat is not being used.

The problem with battery discussions on here is that they are dominated by heavy users, either because they have lots of power hungry gear, sail away from shorepower for long periods, or liveaboard. Their requirements are very different from boats with modest power demands who go out for days, wekeends and the odd longer cruise once or twice a year. Expensive AGMS (or heavy duty FLAS like Trojans) and lithium are a waste of money - a solution waiting for a problem for most users.
 
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simonfraser said:
indeed looks too good, but its the TN Power AGM or optima yellow tops i recon
as said can not top them up where they are going to be
draw is 2 ish amps for 2-3 days

was thinking of getting a set of AGM's that would mean solar def not needed and charge when back ashore
Click to expand...

How many AH are you thinking of installing Simon ?
 
simonfraser said:
2Ahx24 for a day
3 days max without running the motor
Say 150 Ah
Two yellow optima will do that no prob as far as I can see

The lead has been wound and is supported by the matting
They claim less weight, C20 40 ish
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How do you propose to squeeze 150ah from a pair of Optima yellows ?

The largest capacity they do is the 5.5, which is 75ah, so you'd need four of those, at circa £230/£240 each.

If you are going to use 150ah with no input you'll need at least 300ah of capacity.
 
ok, clear this up for me:

this yellow top
has a C20 of 55Ah (£170)

what does C20 mean
'The C rating of a battery quantifies the total the amount of current (amps) that can be delivered over a length of time '

so if i ran the yellow top down to zero i could get 55Ah out of it ?

if i take 3A per hour out of it, that would last 18 hrs ?
running it down to 50% 9 hrs ?
 
That battery is a stop/start battery for a small petrol cat like my 1l C Max and not really suitable as a domestic circuits battery. You can use a similar battery of greater AH capacity - I have 3*95aH for my house bank and one each of the same size for engine start and Bow thruster. Bit OTT for engine start but fine for house and BT. For house service batteries you need to be looking for a bank roughly twice the nominal capacity of your expected maximum usage before recharging (that is 50% depth of discharge). Therefore, as Paul says you need a 300AH or so for your needs and you can achieve this with FLA or AGM, but as I explained in post#6 ultimate life (number of cycles) is longer with AGMs and the increased performance is usually greater than the increased cost, particularly if you use those stop/start AGMs. The Optima one is expensive, although the claim is twice the cycles of a typical FLA - but more than twice the price!. There are other much cheaper AGMs which have a premium of roughly 50% over a good FLA, but also claim over twice the number of cycles.
 
simonfraser said:
ok, clear this up for me:

this yellow top
has a C20 of 55Ah (£170)

what does C20 mean
'The C rating of a battery quantifies the total the amount of current (amps) that can be delivered over a length of time '

so if i ran the yellow top down to zero i could get 55Ah out of it ?

if i take 3A per hour out of it, that would last 18 hrs ?
running it down to 50% 9 hrs ?
Click to expand...

Simon, you cannot run those down to zero, unless you want to change them every few weeks. 50% DOD max, as i said, you need 300ah of capacity without any charging.

For the uses you have given here, all you need is 300ah of sealed lead acid. If you can find some sensible AGMs, where the long term cost of ownership is similar, go for those, but again, you need 300ah.
 
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