Re: battery charging

If the charger is current limited (internal circuitry limits output to about 270 ma regardless of terminal voltage) you could simply hook it and it'll work. But be careful if you do this: If left charging too long (ie. weeks) it could slowly boil the battery dry.

OTOH if the charger is NOT current limited it'll supply more than it's rated current when connected to a 6 volt battery. Consequently it'll overheat in very short order.

If this is the case you could again add a series resistance to limit charging current to a little over the self-discharge rate of the 6 volt battery. Without doing any calculations I guess a #194 lamp (12 volt side marker/instrument panel bulb) would be about right - but this is just a quick guess.

If you feel the need to charge the battery, my recommendation would be to charge it at the low rate for 24 hours once every 1-2 months.

Incidentally I own a couple 6 volt tractors. They sit unstarted/uncharged from mid-December until late April/early May. But unless one has a battery that's about worn out they always start up unassisted every spring. Seems there's no harm from just letting them sit.

1 - The 12 volt bulb limits max charging current to a lower level - about 3 amps or so. Thus less chance of harming the battery as it reaches full charge.

2 - If the battery fails short or there's otherwise a short in the charging circuit, a 12 volt lamp will simply light up normally. OTOH a 6 volt lamp will burn out almost instantly - it becomes essentially a rather expensive fuse.

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BTW your advice to not leave a 6 volt battery charging in the manner unattended is very good indeed!