DIY Optima Battery Mount & Damn Mice! - 986 Forum - The Community for Porsche Boxster & Cayman Owners

Factory battery was seriously tired after 6 years and a prolonged "no drive, no tender" period. Decided to replace with Optima red top 34R after a no-start stranding. Googling and search on this site led to http://www.dietersmotorsports.com/tech/2002/02-2003.htm . The solution offered was an aluminum plate to mount the battery to... measuring 6.25" x 12". No aluminum plate stock hanging around, but I did have an old piece of polycarbonate (aka Plexiglass/Lexan). Good deal - strong, able to be cut with my table saw and non-corrosive. OK! Cut a piece to the dimensions above, trial fitted to the car. Didn't look right to me. Plate was close to but narrower than the battery base's width with excess spacing to the tray edges. Little to no clearance from the adjacent plate edge for the hold-down bolt hole. Considering the idea is for the plate edge to engage the lip on the battery tray, fitting solely to the narrow side's lip seemed wrong. Another issue was the placement of the battery mounting holes recommended by Dieters... which put the battery too far to the negative terminal side. IMO, some dimensional changes were needed. My end result was a 6.875" x 12.5" plate, with two corners knocked off to allow for the radiused corners on the tray. Other key dimensions noted on the picture (hole locations are edge to center line). Note the battery hole pattern shifts the battery forward to clear the rear lip and towards the positive terminal anchor point. This allows for use of the existing cables with just a slight rotation of the positive cable mount on the firewall stud. Plate fits well under the two lips on the rear and "negative terminal" edges of the battery tray and fills the full width of the tray. M6x30 stainless machine screws, lock nuts and washers hold the battery to the plate and the factory battery retainer M8 bolt (with added lockwasher and flat washer) holds it down. Worked a charm - photos below. In some some shots you'll see remnants of the off season party held by some mice this winter (didn't do the moth crystals trick this one time). They chewed up both plastic foam and fibre insulation plus apparently raided the bird feed at some point and left their empties behind.

Finished product...

Positive terminal adjustment - rotated CCW.

Battery tray detail - front "negative" corner. Note overhanging lip on the outboard side (there is a similar lip on the rear edge) as well as the amount of free width when compared to the Optima battery case shown in place but not mounted on the plate.

Battery on plate and bolted down.

BTW, I made a second full-size completed plate while I was at it. It isn't perfect - there are some scratches, etc. but it is structurally OK. If you're interested in that or the smaller "Dieter-sized" blank (the left one in the first photo), I'll send within the US if you pay the shipping. PM me and we'll exchange pay pal details.

Dude, looks great! I'll be doing this soon. I don't want to ever get stranded with a dead battery. Freaks me out to think about it! Thanks for leading the way...

@ donv, Where did you get the battery from? Did you happen to weigh the Optima compared to whatever was in the before?

I got it from autobarn.com, but did the actual purchase through http://shop.com/ . It was cheaper that way... $139.95 (lower price than direct via autobarn.com) plus free shipping if the order was over $150. I added a 32oz bottle of StaBil to the order and it totaled ~$153. Shipping was fast, ordered 4/1, received 4/4/07 (3 biz days, NY to MA via UPS). I didn't weigh the Optima, but I recall from my web search that many claim the Optima to be a lighter replacement and others say it is not always the case. I was able to weigh the old battery - 40 lbs. on a bathroom scale. UPS claimed 43 lbs shipping weight on the Optima with the Optima accessories (adaptor tray and clips), packing material, StaBil, etc. The StaBil, Optima accessories and packaging run ~4 lbs, so I'm guessing we're at about a wash on weight. I do know it is a smaller unit than the original battery - I got the revised plate width by measuring the base of the original battery. Here's a shot of the one I took out, the factory battery from 2001. Actual orientation is reversed when in the car, posts are to the rear.