Batteries

So our new to us 2003 30' Mainship gets splashed next week. Had the two DEKA 8A27M AGM batteries on the charging system with shore (driveway) power over the winter. They seem to hold a charge with no problem. All winter the lights and stereo were used as I worked on making her our own. Ran the 315 Yanmar for 10 min yesterday and she cranked over instantly and strongly. When we purchased the rig last September one of my question to the broker was battery age. He said the PO has owned the boat for 3 years and never changed the batteries. So this tells me they are at least 4 years old. I will go for two new 8A27M's at $265- each if I must but I feel the old batteries have some life left. But.....I don't want to do an over nighter and find the batteries can't turn over the 315 in the morning (no gen set). What would you do? thanks

regards Holty

any experience with the compact battery jumpers?

My two bow thruster AGMs were kaput after 5 years. Given yours are of unknown age I'd suggest a fresh set.

Once the boat is in the water, just spend night on the boat, at the dock or mooring, to simulate your overnighter. FWIW, on my sailboat with two batteries, I would always select just one battery to use for house and anchor light loads overnight and keep the the other battery as a start. That way I didn't have to worry about starting the engine in the morning.

The other option is to get someone to load test the batteries for you.

I think from reading the model numbers that those are Group 27 batteries. They are a little small for starting a Yanmar 6LP. They may continue to work fine, but if you are going to replace someday, replace them with Group 31 AGMs for more starting CCA amps and more amp hour capacity at anchor.

The whole subject of isolating batteries for overnight house use can run to a chapter or more in a book, so get a copy of Nigel Calders electrical book and read it thoroughly.

More than likely one of your batteries is connected to the 1 position of the big red, round 1,2,all,off switch and the other to the 2 position. The engine starter and the house loads are connected to the common position. Use this switch to select which battery to save while at anchor as suggested in the pp.

David

The life of AGM batteries varies considerably depending on how many times they've been drawn down below 50% charge, so it's tough to say how long they'll go for.

Dave's suggestion regarding a load test at the dock is a good one. You could even do it in your driveway. The stereo and LED lights won't be using much power, but the fridge will be the real test.
Don't waste your money on the compact jumpers. They are ok for a small gasoline engine, but not a diesel.

So I found the Deka's for $175 locally. This rig does not have an A-B- Both battery switch only an on-off switch for both under the sink in the galley. Batteries appear to be wired in parallel. Will look into it further in the morning.

regards Holty

If you have an on-off switch for each battery, you can use them like a single 1,2,all,off switch.

David

Agreed David but there is only one on- off switch. A simple fix would be to isolate the battery with the single terminals with it's own on -off switch.

regards Holty

Since with only one on off switch for two batteries you have no isolation, then I would recommend reading Calders book before I did anything more. You may want to add more house batteries or install a set and forget ACR type system.

I am really surprised Mainship built it that way!

David

"The other option is to get someone to load test the batteries for you."

The folks with the good batt testers are at the golf cart shop.

Fully charged or near dead , their equipment can read the life left in your set.

PIA to drag them out but thats the price for reality.

Found the DEKA Intimidator 31AGM for $210 locally so I grabbed them. They are about 70 lbs each and it was no easy task pulling the old ones out and dropping the new ones in through the small door under the step down. Added a single on-off switch next to the step down to isolate one battery when overnighting. Splash is this Wed. Thanks for the tips.

regards Holty

surprised as well that Mainship wired it with only a single on-off for two batteries. My 26 Shamrock had twin batteries with A-B-Both switch.

My East Penn 230ah golf carts are entering their 5th year, 2 pairs operated in series parallel. Prior to installing solar along with a MorningStar Pro 30 PWM controller, I manually equalized them at least once a month during the seasons. I don't know how often the Pro 30 equalizes although I believe it does so often.

I praise the solar controller! The fluid level in the cells requires adding water about once each season and not much of it, no rapid boiling the stuff off. I am convinced that equalization is the secrete to long battery life along with keeping the batteries fully charged. Of course, gels/agms are a different matter.

I just purchased an MPPT Victron 150/70t ... changed my mind from the 150/85t, just didn't see the need for the additional capacity offered by the 150/85t. But back to batteries. I might add more this season. If so I will wire it as a new bank to avoid mixing old ones with new. I am pleased the East Penn golf carts and any additions to my system will be East Penns. One other feature I like about old style lead/acid (flooded) is I get to use an hydrometer to see each cell's charge condition; cannot do that with other styles.

foggysail said:

One other feature I like about old style lead/acid is I get to use an hydrometer to see each cell's charge condition; cannot do that with gel styles.

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I will bet you still own a slide rule and know how to use it (as I do)!

GoneFarrell said:

I will bet you still own a slide rule and know how to use it (as I do)!

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How did you know that I have and still use my old K&E log log duplex decitrig? It rests comfortably in my desk's middle drawer and I used it twice already today

Ha! I was a Pickett guy until my grandfather funded an HP45!

Still had to pack the Pickett to class, as the 45 was considered an unfair advantage for tests!

My boat has 7 years on a 2x2 array of US2200 XC wet cells. They are starting to sag...another half a boat buck soon!