2011 04 06
Vero Beach, waiting for the Garhauer Traveler to arrive.
Before we set off for the Caribbean the Budget Committee authorized the purchase of a new start battery. I have come to question the value of keeping a single battery separate from the house bank the sole purpose of which is to start your boat. Not that I can admit this to the BC. I spent money on this thing.
The theory behind having a battery that you keep isolated from all the others is that if you drain your house battery bank some day by, say, using the breadmaker and the Mr. Coffee on the same morning you will still have one battery kept separate from the others which will be fresh and ready to start your diesel. You will not be stranded.
The Honda generator has blown this to bits.
With the huge number of cruisers carrying a pull start Honda generator these days the logic of the "failsafe" starting battery theory sort of begins to unravel. When the house bank is over taxed by your excessive use of the comforts of home you just get the Honda out of storage, pull the cord and wait an hour.
One morning on starting our diesel to leave the anchorage we discovered our alternator had failed. The diesel started fine but our batteries suffered a constant current drain - the fuel pump, engine panel and our instruments alone had a current draw in the order of 5 amps. We had been at anchor and not charging for two days so the batteries were less than full.
Faced with a full day of motoring, a partially drained battery bank and no functioning alternator we got out the Honda and ran the Honda to fill the batteries while the diesel provided propulsion.
You are getting the idea - a Honda generator is far more useful and valuable and reliable than keeping a battery isolated from all the others just for the purpose of emergency starts.
One boat we know holds the Honda in such high regard that they keep one on board and use it regularly even though they have a factory installed $15,000 Panda genset. The Honda is more efficient, runs quieter and with less vibration than its (much) bigger brother.
Dispensing with the separate start battery is a good idea for other reasons as well:
1. if the start battery were tied into the house bank your overall battery capacity would be bigger and you would then be less likely to drain it so low it would not start
2. most people realizing the start battery will be lightly used and rarely called on tend to cheap out on this item. There are a huge number of big AGM battery banks found on boats using an el cheapo Walmart wet cell as their emergency backup. This logic is highly suspect. Your emergency backup should be the best you have - like your storm anchor.
3. using a different battery type for a start battery causes problems with the charging profile and you are likely to bake the start battery if you are not very careful in setting up the charging relays - especially if you are using AGM for the house bank and wet cell for the start battery
None of which has anything to do with the intended post, which was to be a real world discussion of battery cable corrosion. I guess I will leave that for next time.