Replacing batteries

[suiramor]

I have four 4D house batteries. Two definitely need replacing (I didn't know they were there and let them dry up) and two (Excide NG-4D) seem still somewhat OK. I am told I can replace them with Lifeline GPL-4DL AGM but that seems like a rather expensive option ($650 each). Can I replace just two batteries and keep the older ones on same network - charger and inverter? What do I give up by looking for some less expensive alternatives?

[newhaul]

Originally Posted by suiramor

I have four 4D house batteries. Two definitely need replacing (I didn't know they were there and let them dry up) and two (Excide NG-4D) seem still somewhat OK. I am told I can replace them with Lifeline GPL-4DL AGM but that seems like a rather expensive option ($650 each). Can I replace just two batteries and keep the older ones on same network - charger and inverter? What do I give up by looking for some less expensive alternatives?

If you are wanting to stay with fla then 8 new gc2 batteries would be a much better choice than agm.
( 6 volt golf cart batteries )

[Adelie]

Unless you have specific need of high current discharge I don’t see an advantage to AGMs.

There are 2 significant problems with AGMs as I see it:
A. They need to regularly be CHARGED at high current. This applies to Carbon Foam AGMs too. If you are regularly taking them down to 50% then they should be recharged at 0.2C minimum and 0.3-0.4C would be preferred. For a bank sized for cruising that means and high output alternator (=>120A), regulator and serpentine belts. For bigger banks you may need to split it in halves and charge each half at high amps.
If you normally only draw down to 75-80%SoC and occasionally lower you are probably fine with just solar and the stock alternator on your engine.
B. They really don’t like Partial State of Charge (PSoC) operation. That is they are not charged to 100% every cycle but only to 80,85,95% before being drawn back down again. Carbon Foam, Gel & FLA do much better with PSoC.

I would look at Trojan Golf cart or solar batteries. They are guaranteed to be try deep cycle batteries.

I have 2 T-1275s on my boat, mostly for electric propulsion.

[Paul L]

Originally Posted by suiramor

I have four 4D house batteries. Two definitely need replacing (I didn't know they were there and let them dry up) and two (Excide NG-4D) seem still somewhat OK. I am told I can replace them with Lifeline GPL-4DL AGM but that seems like a rather expensive option ($650 each). Can I replace just two batteries and keep the older ones on same network - charger and inverter? What do I give up by looking for some less expensive alternatives?

If you are just looking to delay the inevitable cost of replacing the batteries and are not going to be putting them into heavy service or service in remote places --- you could remove the two dead 4Ds and just run your system off the two good ones.

[ranger58sb]

Originally Posted by suiramor

I have four 4D house batteries. Two definitely need replacing (I didn't know they were there and let them dry up) and two (Excide NG-4D) seem still somewhat OK. I am told I can replace them with Lifeline GPL-4DL AGM but that seems like a rather expensive option ($650 each). Can I replace just two batteries and keep the older ones on same network - charger and inverter? What do I give up by looking for some less expensive alternatives?

Are you considering AGM because at least two of the batteries are in a location where it's difficult to service them?

Otherwise, flooded 4Ds aren't uncommon...

Were it me, I'd replace all four at once if they're all part of the same bank.

-Chris

[skipmac]

I will second the previous recommendations.

AGMs. Unless you have specific needs like very high amp draw on your system or very hard location to access every few months to check water AND you have a high output charging system AND a way to frequently fully charge AGM batteries then I see no justification for paying the large premium for AGMs over regular FLA (flooded lead acid) deep cycle batteries.

The most bang for the buck and the least likely to cause permanent back injuries are 6V GC2 golf cart batteries (60 lbs vs 160 lbs). They are true deep cycle, are reasonably tolerant of abuse and much cheaper than AGMs. They will require a slight modification to the wiring so you can link them in serial in pairs to get 12V.

[tkeithlu]

Ditto on Skipmac and preceding. Within those recommendations recent threads have made positive noises about Duracell batteries from Sam's Club.

[sailorboy1]

Originally Posted by suiramor

Can I replace just two batteries and keep the older ones on same network - charger and inverter? What do I give up by looking for some less expensive alternatives?

Yes you can. Don't get dragged down the rabbit hole.

You can replace the 2 bad batteries with any you want to. Yes there are cons. but if all you want is to get the bads one out and new in, just replace them.

Cheapest would be 4 GC2 golf cart batteries, but 2 4D sealed are ok if you don't what to spent the $$$$ for AGM (waste of money no matter what IMO)

[skipmac]

Originally Posted by tkeithlu

Ditto on Skipmac and preceding. Within those recommendations recent threads have made positive noises about Duracell batteries from Sam's Club.

Oddly enough these are the exact batteries I have on the boat. Three years and seem to be just like new so far. As I recall they were about $90 each at Sams so $540 for 660 amp hours rated capacity in the house bank.

[suiramor]

Thanks for such helpful replies. I will stay with 12V (+20" in length) for now to avoid yet another project needed to change the battery seating (size). I have not been able to find a Duracell in that format so looking at a Dyno Heavy Duty 4D Marine Battery - 12V Deep Cycle, 180 Amp-Hr ($340). Seems reasonable?
My use of power is on the lower end: seldom use auto-pilot, occasionally fridge and would like to be able to re-charge, at least partially with solar/wind (my next project). I have no problem with access to the battery (now that I found their location ).

[Cheechako]

Originally Posted by suiramor

I have four 4D house batteries. Two definitely need replacing (I didn't know they were there and let them dry up) and two (Excide NG-4D) seem still somewhat OK. I am told I can replace them with Lifeline GPL-4DL AGM but that seems like a rather expensive option ($650 each). Can I replace just two batteries and keep the older ones on same network - charger and inverter? What do I give up by looking for some less expensive alternatives?

Yes you can replace just two , although it goes against what many people recommend. I have done it with no ill effects.
Just make the two you keep are in good shape:
Charge fully, measure voltage after they sit an hour not connected. Measure voltage next morning or day. They should read near the same.
You can get wet cell batteries a lot cheaper.