Need to replace Lead Acid batteries. AGM or Gel?

[tudorsailor]

I currently have Varta Deep Cycle batteries. There are two banks of 4 x 6v so giving 24v with a total (apparently) of 460Ahr. They are 7 years old and are now drinking loads of water - which I take to be a sign that they need replacing

It would be nice to have "sealed" batteries and have been reading about gel and AGM

Is it correct that gel needs the correct type of battery charger and also regulator on the alternator regulator, whereas the AGM does not? Given that the charger and alternator are from 2001, I do wish to find that they damage the gel batteries should I buy them?

I would be grateful for any advice

Thanks

TudorSailor

 

[pvb]

All batteries last better if they're charged according to manufacturer's specs, however gel batteries are particularly fussy. I'd go for AGMs, which are better value. But you still need to check that your charging voltage is appropriate. If your charger was made in 2001, it should have an AGM setting. Similarly, if you have an add-on regulator, that should be adjustable too.

 

[vyv_cox]

Open cell batteries need topping up with water pretty much according to how much charging they get. The Sterling instructions warn that this will happen after fitting one of their units. I also found that water consumption increased after adding capacity to my solar panels. I don't think your water usage is anything to do with the age of the batteries.

Gel batteries are pretty poor in my experience. No comparison with AGM.

 

[Fendant]

If you switch to AGM you need to switch to a suitable alternator regulator and a suitable charger. Mine are both from Sterling.
AGM's are great for winterising without charging for several months. But wrong charging will depreciate their value within hours.

 

[charles_reed]

Open cell batteries need topping up with water pretty much according to how much charging they get. The Sterling instructions warn that this will happen after fitting one of their units. I also found that water consumption increased after adding capacity to my solar panels. I don't think your water usage is anything to do with the age of the batteries.

Gel batteries are pretty poor in my experience. No comparison with AGM.

Agreed - if water usage is the only sign of battery state, I'd suspect you're being a trifle pessimistic.
If the current open batteries are using a lot of water it may be because they're doing a lot of work.
Replacing them with sealed batteries would be a very retrograde step. Sealed batteries don't take well to high discharge/charge rates.
Check, by other means, that the batteries are knackered and think seriously about replacing them with sealed batteries (which are not necassarily AGM or gel).

 

[pvb]

Replacing them with sealed batteries would be a very retrograde step. Sealed batteries don't take well to high discharge/charge rates.

Old wives' tales. AGM batteries are well suited to high current loads, and also accept high charging currents very readily (another reason why they're good for boat use, where engine running times may be limited). A decent AGM battery should last 500-600 cycles as long as it isn't discharged below 50%.

 

[Jeva]

If you can pick up a Victron catalogue they have a very interesting article on the differences between AGM and Gel. For my money Gel are more expensive but will last longer - in the past I've known them last 10 years or more.

 

[pyrojames]

I currently have Varta Deep Cycle batteries. There are two banks of 4 x 6v so giving 24v with a total (apparently) of 460Ahr. They are 7 years old and are now drinking loads of water - which I take to be a sign that they need replacing

It would be nice to have "sealed" batteries and have been reading about gel and AGM

Is it correct that gel needs the correct type of battery charger and also regulator on the alternator regulator, whereas the AGM does not? Given that the charger and alternator are from 2001, I do wish to find that they damage the gel batteries should I buy them?

I would be grateful for any advice

Thanks

TudorSailor

If they are 6v in series then you will get 24vdc, but unless they are huge batteries I'd be very surprised if you have 460 aH. It is much more likely you have 24vdc and 115 ah, or 12 vac and 230 ah, or unlikely (parallel) 6vdc and 460 ah.

Actually, just looked at your profile, maybe there are big!

 

[GrahamM376]

If they are 6v in series then you will get 24vdc, but unless they are huge batteries I'd be very surprised if you have 460 aH. It is much more likely you have 24vdc and 115 ah, or 12 vac and 230 ah, or unlikely (parallel) 6vdc and 460 ah.

Actually, just looked at your profile, maybe there are big!

Why the query about his battery capacity?

I have 4 x 6v in 2 banks of 2 which gives me 480AH total. He says he has 2 banks of 4 x 6v so should have even more.

 

[Beyondhelp]

Your batteries are 240Ah then? Only mention this as some people think you add the AH when wiring batteries in series, but you only add the Ah up if wiring in parallel.

 

[pvb]

Your batteries are 240Ah then?

Lots of 6v batteries are around this capacity. Trojan 125s are 240Ah.

 

[pyrojames]

My error, I didn't read the "two banks" bit, but did realise post post that an Oyster was quite likely to have a large ah!

 

[GrahamM376]

Your batteries are 240Ah then? Only mention this as some people think you add the AH when wiring batteries in series, but you only add the Ah up if wiring in parallel.

Yes, as pvb suggested, Trojan T125.

 

[prv]

To return to the original question -

Traditional flooded batteries are good. AGM have several further advantages over them, for a price. Gel was an intermediate technology before AGM came along, and have nothing much to recommend them now.

Pete

 

[tudorsailor]

Agreed - if water usage is the only sign of battery state, I'd suspect you're being a trifle pessimistic.
If the current open batteries are using a lot of water it may be because they're doing a lot of work.
Replacing them with sealed batteries would be a very retrograde step. Sealed batteries don't take well to high discharge/charge rates.
Check, by other means, that the batteries are knackered and think seriously about replacing them with sealed batteries (which are not necassarily AGM or gel).

What is the best way to test whether or not the batteries are truly knackered? I assume I get the local engineer to test with a "professional" battery tester??

When I bought the yacht (pre-owned as Oyster like to say), the batteries drank increasing amounts of water over the first year of my ownership. Once I had a new set, I hardly ever had to top up with water - although I did keep checking. The current Varta batteries are 7 years old and have lived in the Med all this time. During last summer the batteries seemed to get ever so thirsty and I went through many litres of distilled water - just as I did before replacing them 7 years ago.

Can one get sealed lead acid wet batteries in 6V???

Thanks for all the input

TS

 

[GrahamM376]

What is the best way to test whether or not the batteries are truly knackered? I assume I get the local engineer to test with a "professional" battery tester??TS

Do you have a battery monitor with volt meter? Sounds as if you may have over voltage causing water loss, maybe a faulty regulator?

 

[tudorsailor]

Yes I have a mastervolt panel which displays battery voltage if required. How much above 24v is "over voltage"? In truth I cannot remember what it displays when charging. Can I or electrician easily check the regulator?

Sorry to appear so dim, but electrics is not my forte (obviously).

TudorSailor

 

[prv]

Can one get sealed lead acid wet batteries in 6V???

Sealed wet batteries are basically exactly the same as your current ones but without the ability to add water. They have a bit of extra headroom in the case so that they can hold a bit more water in the first place, but once it's used up they're done for. Basically designed to appeal to people who would be scared of having to open the caps on a normal battery, and not really a sensible proposition for serious use.

If you want genuinely sealed/spill-proof/no-maintenance then you need AGM. Otherwise stick with good-quality traditional flooded.

Pete

 

[vyv_cox]

Sealed wet batteries are basically exactly the same as your current ones but without the ability to add water. They have a bit of extra headroom in the case so that they can hold a bit more water in the first place, but once it's used up they're done for. Basically designed to appeal to people who would be scared of having to open the caps on a normal battery, and not really a sensible proposition for serious use.

Sort of true except that the charging voltage is reduced a little with sealed batteries to prevent gassing. I needed to replace three open cell batteries in a hurry in Greece. I had the choice of sealed Bosch ones to take away, or wait about a week for the open ones to be sent from Athens for quite a lot more money. Naturally, I took the sealed ones. That was four years ago and they still seem to be performing well. Many liveaboards only reckon to get three years out of a bank anyway in view of the daily charge/discharge, so I think mine have done fairly well. My open cell ones did six years but were pretty tired in the end.

 

[GrahamM376]

Yes I have a mastervolt panel which displays battery voltage if required. How much above 24v is "over voltage"? In truth I cannot remember what it displays when charging. Can I or electrician easily check the regulator?

Sorry to appear so dim, but electrics is not my forte (obviously).

TudorSailor

I'm used to 12v but assume you can double up my rates for your 24v?

Unless a Sterling or similar booster fitted, I wouldn't expect engine alternator to put anything over 14.2 - 14.3v and solar/windgen/mains charger around 14.4v then dropping to float around 13.8v.