Lawnmower-type battery for starting small diesel?

Gene Neill

Gene Neill

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Sep 30, 2013
3,541
1988 Catalina 22 North Florida
My Beta 14 (Kubota) engine recommends 350-400 CCA for starting. To me, that's what I consider a lawnmower battery, no need for the weight of a group 24. Boat is 27', displaces 5100, every ounce matters. I myself might forgo a starting battery altogether and just use the house bank, but the wife would probably not like it.

Any reason a small "lawn and garden" battery could not be wired from the charge bus and through a VSR just like a group 24 might be? Fused at the bus and at the battery?
 
jviss

jviss

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Feb 5, 2004
6,745
Tartan 3800 20 Westport, MA
You are correct. I found that the battery used in the tractor my Universal M25, a.k.a. Kubota D850 was designed for used a U1 size battery. That's what I put in as my engine battery, a VRLA U1. Works great.
 
jssailem

jssailem

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Oct 22, 2014
21,104
CAL 35 Cruiser #21 moored EVERETT WA
12V battery. ACR provides power between house and starter. Need to check start battery charging profile.
 
D

dlochner

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Jan 11, 2014
11,423
Sabre 362 113 Fair Haven, NY
A few things to consider.

With a small capacity battery, like a lawnmower battery, how deeply will it be discharged on each start? A Group 24 battery will have very little reduction in its capacity. If the battery is at 100% SOC after starting the diesel it will be at something like 95% SOC. What is the amp hour capacity of a lawn mower battery and how much of that capacity will be used on a simple start? What if it takes a couple of tries to get it started?

Second, how much back up battery capacity do you need if the main house bank fails? A Group 24 will start the diesel and provide a decent supply of electricity to use the VHF, light the running lights, or keep the GPS working.

If saving weight is an issue, what else can you jettison to reduce weight that will have fewer adverse consequences? A Group 24 battery is maybe 50 lbs, a lawnmower battery is maybe 10 pounds, the 40 pound difference is less than 1 % of your boat's weight. If you are racing in a highly competitive fleet with money on the line, a 1% weight reduction is significant. For the rest of us, not so much.

So, to answer your original question, yeah, you could install it as you asked, but is it worth it?
 
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jviss

jviss

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Feb 5, 2004
6,745
Tartan 3800 20 Westport, MA
A small tractor battery, like a U1size, will start that diesel dozens of times before charging.

It's not so much weight, but size.
 
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