We're big believers in flooded 6V golf cart batteries connected series-parallel to create a 12V bank for house batteries. Nothing can beat them for cost per Ah, and as long as they are cared for and never discharged below around 50%, they last a very long time. The big problem for flooded lead-acid batteries is they require maintenance - namely, topping off regularly with distilled water. On Jane'O, while our batteries aren't horribly inaccessible, getting in to where the batteries are to see the water level and top them off to the right level is difficult enough that we admit to not taking very good care of them.
Another reason to stick with old-school flooded batteries - although Gel and AGM batteries require no maintenance, you can't mix different types of batteries on a single charging system - which means we would not only have to change out the engine and generator starting batteries, but also have to recalibrate our battery monitor, AC charging system, and both engine alternator regulators to the different type of batteries. And these batteries can be 2 to 3 times the cost of golf cart batteries.
While doing some research on which batteries to use, we came across battery watering systems that make topping off the water of every battery as simple as connecting a single tube and waiting a minute or two - and the entire bank is topped off to the right level every time. While not a cheap system, it was a no brainer for us, that should ensure our new bank lasts at least as long as the old one.
So, this was the right choice for us - replace the existing 4 golf cart batteries with 4 new ones, and install a watering system to keep the water levels properly maintained. We also replaced all the battery cross-connect cables, as the old ones were, well... old... and some of the crimps had started to loosen.
We went with US Battery 2200XC batteries, which are 232Ah at 6V each, giving a total bank capacity of 464Ah at 12V - slightly higher than the old batteries, but not by much. They were purchased from a local golf cart shop, making it easy and relatively cheap. These are off the shelf batteries using standard battery posts - which means they are available anywhere. The only thing I had to do to the battery monitor was give it the new total bank capacity, and set the Peukert Exponent for these batteries. No changes to the charger or engine alternator regulators was needed.
As far as the battery cable cross-connects go, instead of connecting a single cable for each series pair, as is commonly done (and was the previous configuration), we instead cross-connected them as suggested by Nigel Calder.
This is the common way that a series-parallel connection is done, but it can cause one of the series pairs to work harder than the other, especially if something goes wrong with one of the series jumpers (this actually happened to us in Mexico). Forgive my butchering, as well as copying Mr. Calder's drawings without his consent.
|The usual cross-connect method|
|A better cross-connect method|
These drawings are copied from Nigel Calder's excellent book "Boatowner's Mechanical And Electrical Manual".
Here's a few pictures of the installation, including the battery watering system and making the new cross-connects.
|Crimping a lug with an excellent, but overpriced Ancor crimping tool using a vice|
|Completed cross-connects, 1/0 cable with adhesive heat-shrink|
|New battery, note the SpeedCap, which is about to be removed for the watering caps|
|The white SpeedCap has been replaced with three black watering caps|
|The bank nearly ready to be installed, staged in the cockpit with the same spacing as it will have in the engine roon|
|Watering tank, filled with distilled water|
|Flow indicator. When this doohickey stops spinning, the batteries are ready to go|
|Tired old batteries and cables. Note that one of the cross-connects was simply taped with blue tape, instead of done with adhesive heat-shrink|