This winter I am hoping to tackle a 4 phased upgrade to Insolita’s charging and battery systems.

Going into this project, Insolta is sporting, nearly, her original power systems. That is to say that she has 2 group 27 batteries mounted on the bulkhead under the cockpit. She has a simple 10AMP shore charger & her originally spec’d 35AMP alternator. By the time the flowers start blooming I’m hoping to have upgraded the battery capacity, as well as the wiring, get a better sized, more appropriate shore charger, a better alternator solution, and a smaller solar array to augment the alternator.

PHASE 1 – Adding capacity.

I’m not sure this is the right phase to tackle first, but the boat told me that the old batteries we’re done, and that I had to do something wether I wanted to or not. When we came out of the yard in November it was easy to see that the batteries were on their last leg. They were 2 Group 27 [90 AMP Hour] West Marine brand FLA [Flooded lead acid] batteries. A total of 180 A/H [That’s AMP Hours, a measurement of power over time]. They had been in for nearly 4 years, and although they don’t see a lot of extended cycling they certainly had their share of abuse while I’d been learning how to treat them nicely. A toasted alternator, weak charger, and not knowing that they needed occasional watering, and I think they did okay.

I want to add a bunch more capacity, which is actually pretty easy to do. The existing battery shelves and boxes we’re already set up for Group 31s, so just by buying the right size battery for the space, I could add 40 A/H of capacity. A flooded lead acid battery’s useable power is about 1/2 of it’s available amp hours. So previously it would have seemed that would be 90 A/H, except, one of those batteries is being kept in reserve to start the engine if I do something silly like run the “House” bank [what we call the batteries that the boat uses at anchor] dead. So I only really start with 1 battery, or 90 A/H, and 1/2 of that is about 45 A/H.

So the initial offer to the battery gods is going to be replacing the dying lead acid group 27s with 2 shiny and new group 31 AGM batteries. I decided if I’m going to do it, I’m going to do it right, there is no point, ever, spending some money on an okay solution, when you can spend a bit more for the right solution. So moving up to the AGMs, means I can charge them faster, cycle them longer, and discharge them more deeply. I decided on Lifeline batteries. So 2 new G31 batts will take me from 180 [45 useable] amp hours to 220 [55 useable]. That’s okay, a 20% increase. However if I also add in a 3rd battery that will be used as the reserve engine starting battery, I then go to 330 [110 useable] amp hours, and even better, instead of the 50% depth of discharge for the lead acids, AGMs can be discharged to 20% without harm. So now my useable house capacity is 175 amp hours. That’s better, a 350% increase.

There was much thought and research put into where to put the 3rd battery and how to wire the whole thing up. I spent a lot of time reading forum posts, and website articles, chatted with my resident “Captain consultant“. I decided to locate the start battery under the chart table bench. First is terribly convenient to the battery switch which is also located in the same box. There are plenty of bulkhead holes back through to the lazerettes under the cockpit already. Lastly the temperature is fairly regulated; separated from the engine, not too exposed to the outside temps.


So the balance of the wiring with the 3rd battery is pretty straight forward. Wire the 2 existing batteries in parallel. Replace the existing wire runs to the switch and ground, making sure to run “across the bank”, which is to say pull the house positive from one battery and the negative from the other. I decided to wire in a few extras. First, after yet another marina fire this winter, I’m adding MRBFs [marine rated battery fuses] to each of the positive runs. These fuses are ignition protected, and will prevent any open shorts from running away. The fuses are rated at 200AMPs. I’m also going to wire in 2 new bus bars. Each is rated at 300AMPs and will make easier work of some future parts of the overall plan, and should make it easier to wire in another big winter project, the windlass.

Cheers for now.