At 04:14 PM 10/1/03 -0400, Dick Masse wrote:
>"What to do about battery/ies - the frame is new for the 6V batteries but I was hoping I could get a 12V and put it in the existing frame...any thoughts on that?"

Yeah. The 6V batteries sort of suck, to put it mildly. At least half again the cost of 12V, and you need two. They are also mostly old technology type with only moderate cranking power, and have a life expectancy of about 4 years. A single 12V will be about 1/3 the price of two 6's, have way more cold cranking power, will probably last about 6 years, and can be bought with a 72 month prorated warrantee, usually for about $49.99.

The smallest commonly available 12V will not fit in the stock 6V carrier. You need to extend one battery carrier (usually the right side) about 1-1/2" at the back edge (a little cut and weld).

At 05:21 PM 10/3/03 -0400, Dick Masse wrote:
>"I'm adapting the battery box to take a larger battery and it will measure 7.25 x 8.25 x 8. I hope and have a battery selected to fit in there"

Might be asqueaker. Consider leaving space to for the rubber pads on the ends at the bottom.

Find battery size numbers here: www.rtpnet.org/~teaa/bcigroup.html
The smallest standard format 6-volt battery listed there is group 17HF (6V near bottom of list). This one is 6-7/8 wide x 7-3/8 long. The original MGA battery was even smaller. The carrier is barely 6-3/4 wide (maybe 1/16" more) x 7" long. and that included space for rubber pads at the ends. So the original battery was about 6-3/8 wide and not more than 6-1/2 long. Lucas number was SG9E (wet as installed), or STGZ9E (dry charged for export).

Bear in mind that the standard group size dimensions include the larger crown size at the top, and almost all of them are slightly smaller at the bottom with the thin walls. Also beware that new batteries can be had with or without bottom flanges for bolting them down, so be sure to look for one without the bottom flanges. I have (once) cut the bottom flanges off of a battery, but you have to be really careful not to cut through the thin wall of the case.

The smallest current commonly available 12 volt battery is the group 26, which is 6-13/16 wide x 8-3/16" long (7-3/4 tall including the posts). This will be very close to 8" long on the bottom, so the original carrier in the MGA needs to be lengthened about 1-1/2" to accept the battery and the rubber pads. The group 26R is reverse polarity, which is just the same as having the posts on the opposite side of the battery.

>"assuming i can get it by the trunk frame, etc..."

No problem. Just tilt it about 45 degrees and it goes right in.

>"it has 625 CCA I assume that is enough to do the job."

No problem. I think the original batteries were about 300 CCA. About 1 amp per cubic inch of engine displacement is enough in mild weather, so start with 100 amps minimum. But you can de-rate the battery to about 40% of the base current capacity at 0dF, and figure it will take at least 200 amps to crank the engine at that temperature, so that's not much of an excess. At -20dF you can derate the battery to about 25%, and triple the power required to crank the engine, and all bets are off for getting it started. When I was driving my MGA in the winter while in college, with two new 6 volt batteries it would (usually) start okay down to about 0dF. At -10dF it seemed to crank at a reasonable speed, but didn't seem to vaporize the fuel very well, so a sniff of ether was sometimes in order. Starting should always be easier with a modern single 12 volt battery.

>"not like you have to run a lot of accessories off of it...ha!"

I only run a lot of small current draw accessories, like a 2 amp rally computer or laptop computer. Battery powered tire pump might take 4 to 5 amps for several minutes. Battery powered impact wrench for the lug nuts pulls 10 amps, but only for a few seconds at a time. The biggest power hog I ever installed was a 50 watt stereo radio. That would be about 4 amps cranked up to full volume, so not such a big deal. But if you turn everything on at night, ignition, high beam lights, heater and wipers, it's already getting pretty close to the current capacity of the generator, so one might seriously consider not running the radio much. If you don't need to run the wipers, go ahead and run the radio all night. If you want a beefier radio you will need an alternator conversion.

The one significant disadvantage of the single battery is the total power capacity. If you leave the head lights on and walk away, you would be lucky if it starts two hours later. The two 6 volt batteries make a larger physical package that can carry more plates and hold more total energy. That means it can hold up longer in the event of a generator failure or leaving something turned on. In daylight, if you switch off everything except the ignition (coil and fuel pump), you might drive for several hours on a fully charged battery with no charging. With lights on at night, may be two hours tops before you can't see anything in the dim glow and the ignition starts to cut out. With two 6 volt batteries you might get an extra hour of running time.