Alan

Anyone installed an auxilliary/backup battery - for audio or any other purpose?

If yes what did you use and where did you install it? - how/what is it configured to supply? & how is it charged?

Thinking of something like an Odysesy or Hawker gel type mini battery.. anyone? - search reveals nothing like this...

Alan

MGW-Fla

uhhhh with you being one of the main resident 928 electrical gurus Alan, most would probably be looking to you as the pioneer to find that solution for the rest of us!

Alan

Well of course I have some ideas - but interested to see if anyone already did it... Not a high priority but the desert heat kills batteries unpredictably and big audio has its own issues...

Alan

dr bob

Alan--

I remember a custom rear aux battery setup, installed by the Salt Lake City guys IIRC, used to power a TE cooler in the rear lugage area while the engine is off. It used a couple 17ah gelled batteries aft of the tool panel, with a relay for isolation when the engine wasn't running.

Alan

I certainly don't expect to... however you never know...

As you can see with simultaneous threads on battery & alternator - I'm considering some power supply updates...

I've also noted recently in several places - I'm very unhappy with how the cars is wired for the heavy duty power feeders... its all done wrong - just don't know how far I'm going to take it...

Dr Bob - I do remember that thread - but I'm thinking rather higher current than that.. maybe not huge Ah capacity though.

Alan

maroonedlandshark

Why go to two batteries when you can get one large one to do the trick?? 2 weeks ago I had to replace the battery in my shark and I went with a Sears Platnium sealed Die Hard. I went with an oversize battery that just bairley fit in the battery box. I believe the battery was for a 1 ton Ford diesel. It has considerably more cold cranking amps and more storage capacity than the battery made for the 928. I also run a big sound system with dual amps and a sub and wanted something that would last. This battery ran me just about $200.00 and carries a 4 year full replacement warranty with 60 monthes pro-rated after that.

Alan

Well - when one big battery dies you stll have none... that simple...

And they do die regularly especially if its hot... (and its hot here) replacement warranties are good - but not so immediately helpful if it fails when you are in the middle of nowhere...

I also would like to have a battery backup for my clock & ECU mem when I decide to work on the car (elsewhere...). This requires some rewiring work but is very doable if you are willing to change a few things...

1 battery is still a single failure point for me... and I work on my car a lot - little projects for fun...

Alan

V2Rocket

Spare tire?

Alan

Yes Ihave one and plan to keep it... Indeed part of the question is where? but also how is it charged, connected etc...

Alan

Alan

Well after my most recent (almost annual) battery failure and pro-rated replacement - I've decided to move ahead with installing an auxiliary battery so I don't get stuck awaiting my wife's arrival in the truck yet again...

I was planning this anyway (with memories of the last battery failure)... I now have renewed motivation..!

I've yet to have a battery in any of my vehicles in Phoenix last much more than 2 years.

Heat just kills betteries and we have way too much of it - usually the symptoms are dead cells and/or increased internal resistance.

So I'm going to install an Odyssey gel type mini-battery. Capable of starting the car in emergencies but still fairly small and relatively light. Only about 17Ah total capacity (vs 75Ah for the main) but good for >650A cranking (for a little while).

I have figured out how I'm going to charge it and have the parts for that - but for the install location the best I can come up with is in the front fenders ahead of the wheels. The passenger fender would be my choice since I most often travel without a pasenger so this balances slightly better. Its not ideal to add any weight so far forward - but for starting the battery needs to be located where it can be connected with robustly sized and short cables. Other than in the spare tire well (which is fuly occupied) there is no other space I can see that is big enough... Anyone have any other magic ideas?

I know I can fit it in the fender & mount it securely to the main frame very low down and this works well for where the battery changeover switch would need to be (~ where engine jump post is). I'd have to relocate the horns a little and work around some other things I already have in there... but do-able I think...

Its about a 15Lb weight and only ~7" (W) x 3" (D) x 6 1/2" (T) small but not tiny.

Ideas?

Alan

PorKen

You have a manual, so how about in the empty torque converter hump area?

There's room enough for that mid-turbo setup, there.

dr bob

Without measuring-- It seems to me that this is the size that was used with the rear fridge project. They had two of them behind the tool panel cover.

I'm thinking that a big diode or three could charge the thing(s), and a starter relay ala Ford products could be switched only when you decide that the regular battery isn't quite up to the task. I picked up a couple high-current UPS batteries in this exact configuration from an outfit in (drum roll....) Phoenix a month or two ago, about $80 for two. That are rated 18ah each, same physical size as the 17ah one you describe.

Maybe we need to adapt the rear AC unit to cool the battery? Kinda like the fuel cooler thing behind the engine, but in the rear AC suction line. A loop with a glcol mix, a little circ pump, sounds just like the kind of think we need added. Wait a sec... You could add another section of tubing and liquid cool the rear amps. Grind off those heatsinks and solder some tubing to the plates to carry the heat away, and save a lot of space.


Seems like one of those porta-jump boxes might fit inside the spare tire like the factory air compressor does now. Need to measure for sure . In another car I opened one of those bargain-at-Walmart tire compressors and just carried the guts without the case for emergency duty. That might make it small enough to go in the spare with the jumpstart box. Add that 15-bus accessory lighter jack in the spare wheel well and the box would just live there happy until you need it. Plus, if you ever need to give someone else a jump it's always charged and ready with no risk to your 928 electrics. waddya think?

ew928

Too bad it's so thick. Or a false floor in the passenger footwell would hide the battery well.
You can even use the wacky plywood cover and surround to match the fuseboard cover.

Alan. You don't run the Passport 8500 type radar detector, do you?
I've been running mine in battery mode so whenever there's no alert it will give readout from the cigarette lighter voltage. Mine reads about 3/4 volt low. Quite entertaining watching it dip into the upper 11V range at hot idle in traffic jam with AC on. Not.

Dr. Bob, do those jump boxes work on your car?
I've tried using the jump box admittedly from the engine jump post without success.
Maybe attaching the jump box directly to battery might work better.

Alan

.
I went back and looked at those posts. Same technology battery - but this one is bigger - there is no way it would fit behind the tool panel - not even close.. you are right though they had 2 of the smaller ones.

I did consider the booster box thing but I could not find one that would fit - even without compressor. Having it be portable would be a nice extra flexibility... I may do that in my truck - plenty of space to store it.

For charging I'm planning a combo of dual diode pairs and a relay switched after the car warms up (primary charging to the main battery for a few minutes after a cold start).

The Aux battery will only be linked to the starter during starting by means of a manual switch. I already have a main battery off switch if its needed (e.g. for when its sinking current).

I have not built the panel for that yet but I have the parts - it will go at the jump post location and include a new fuse to CE also. I will eventually upgrade the feed wiring there also its not up to spec as far as I'm concerned (16mm^2 is weak for starting duty). I've been taking measuremnents there and its extremely tight for what I want to do - I thnk I have a plan though.

Ken - I have quickly looked and I don't see any way that the hump has enough room - there is volume all around but not all in one place... besides its an exposed hot/cold place at times... not ideal.

Of course inside the fender is a pain to get to also - but its mostly protected from temperature extremes and is very close to the jump post.

Alan

Alan

Ernest - I did consider this - but its way too much room to lose - and its actually a poor place from a wiring point of view. The connections back to the engine jump post are much too small for a starter feed (and really even for their intended purpose too...). Only option would be to route a new at least 4 AWG wire through the firewall & bulkhead - a real pain to do. Overall the front & back of the car are more attractive with battery or starter proximity (or existing connections to those).