Are there any drawbacks to adding a 2nd helper battery up front in the car, like a small odyssey to add additional start and idle capacity on hot days when all the fans are on/etc?

 

It is pretty damn hot in Austin, TX and I have never felt the need for more battery power. If you are having problems keeping a charge or your battery is not cutting it then you have other issues to worry about and adding a 2nd battery is just going to make things more complicated and difficult and you will just be masking your problems, not fixing them.

You should start with a serious cleaning of every ground point on the car and then a new proper size and power battery for the back and then an alternator or serious wiring check-up... Spare battery should not be needed on these cars even with EVERYTHING on...

 

Well...not having a charge problem...and it may be a problem thats not even there for the most part, just helping to counter the voltage drop end to end on the car.

Was just an open thought.

 

Only if you want to add one of those 15,000 watt stereo systems and 3 or 4 more alternators.

 

A sharkwoofer in every door!!


Of course, I could get a 928-Spec. $700 alternator too.

 

I think the only reason to do it would be to have a backup for when the battery fails. You'd then need a switch and charging mechanism for it.

These batteries don't add much extra capacity ~15Ah to the stock 75Ah so the value to me is solely to not be stuck when the heat kills my primary battery - and for sure heat kills batteries - and sometimes they die very fast...

The biggest drawbacks are weight, mounting it solidly and wiring it robustly & safely - without creating new failure mechanisms...

Otherwise I think this is the best location to mount it - its hard to find space anywhere else that is hidden away & not too hot (even in back).
also the balance is reasonable here - its mounted solidly - very low and opposite the driver - more balanced for 1-up situations.

This is configured as an Auxilliary (back-up) battery. Charging system and change-over/supplement/isolate switching.

If you need more power when running - you need a better alternator - the battery shouldn't really be supplying power when the engine is running...

Alan

 

If you have a parts store that will work with you, have them order a Bosch al9960lh alt & see if it will fit physically - might have to work with mountings.
160 amps:


http://ep.yimg.com/ca/I/yhst-1963067...9_2162_5523679

http://www.invasionautoproducts.com/boalfortr.html

Also consider a 4/0 battery cable:

http://gregsmarinewiresupply.com/Zen...&products_id=7

They will make them to length:

http://gregsmarinewiresupply.com/Zen...products_id=62

 

Jeff--

Hot-day charging challenges are par for the course with hot alternators. Adding a bigger alternator won't help if it isn't kept cool. Another battery might stay a little voltage drop between the battery in the rear and the load in the front when it's a hot idle situation, but the available charging current from the alternator is still the same, so it will just take a little longer to bring 2 batteries back to full charge when you do finally get rolling again. The extra battery in the front for that time when the regular battery roasts and fails is adding another battery to roast and fail. With no way to 'test' the Odyssey battery until the primary fails, there's at least a 50-50 chance that the Odyssey has already failed.

So.... Make sure the alternator cooling hose is intact, no tears/leaks/crimps/mice limiting airflow. Look at your alternator with a PM eye, consider removing it an cleaning it thoroughly, refurb the slip rings, add new regulator/brush holder assy, new bearings. Or buy a rebuilt/have yours rebuilt. They do get tired with dirt and age and miles, and it all shows up in the summer AC season when the fans are at full load, heat is highest, traffic seems slowest, etc. Oh-- Put a new belt on and tension it correctly. Thumb pressure deflects a belt thickness, no more. Most ribbed 928 alternator belts I've looked at are way undertensioned -- think banjo-string tight and you'll be getting closer. And yes, that will affect charging rates and no, you don't hear a squeal like a V-belt when they slip at higher loads/RPM's. But you probably knew that already.

I'm working in a place where there are enough generators to make about 14,000,000,000 Watts. Hydrogen-cooled (less aero drag) and brushless exciters. The excitation current in an hour would supply my house for a year... It would have to be a really loooong extension cord though.

 

Dr Bob has a point about failure purely due to heat - but I do think the biggest failure stress issues are from high ambient with high current discharge & recharge cycles - so I think 50/50 is far from realistic...

If the backup battery is constantly recharged but has low supply current draw then it is far less stressed in this regard.

I do agree that options that allow some validation of the status of the back-up battery do make sense (else it may be no back-up). Periodically monitoring the at rest voltage is probably most accurate & predictive, the required changeover switching allows for some ignition or starting load testing - but even connecting a few light load non-critical but functionally visible features to it can also make sense (incl. for other reasons...) - e.g. alarm system, keyless entry, clock...

Alan

 

Bob:

How does it take 2x longer to charge 2 batteries, when during the same time period...you had the same amount of discharge? How does 2 batteries create 2x the refresh time?

 

If only...

If only alternators were 100% conversion efficient. If only batteries were 100% charge efficient. Ever notice that there's heat at the battery, the alternator, conductors? That's the 0efficiency leaking out. So it doesn't mean that it takes 2x the time. It means that if you are somehow able to get two batteries or even just one battery to deliver more power when the alternator isn't keeping up, you'll be making it up later with that same alternator that wouldn't make enough to keep up originally. A bigger battery capacity, regardless of whether it's one or two or more, only smooths out the load vs demand flow a bit. Ultimately it needs to come from somewhere.

-----

We own cars that were electrical pigs when they were built, with lots of new-at-the-time piggy electric features. There's a reason why the cars came with BIG alternators as they had more stuff added. Adding a carputer? A bit of stereo gear? Charging the cellphone and running the GPS and radar detectors? Hot day with the fans running at high speed, AC on and the blower blasting, tired pair of fuel pumps, low-impedance injectors, that high-energy ignition, an older alternator and corroded electrical connections?

My car is sitting quietly at home in the garage under the storage cover, battery disconnected, waiting to rumble to life again in a few days. Seems to do better that way than with the maintainer attached without disconnecting from the car.

 

One reason the 928 battery is in the back, in addition to better weight distribution, is that it doesn't get as hot as a battery in the engine compartment. While there is some voltage drop, most of the operating current supplied is from the alternator which is in front.
Back to cables; both batt hot and grounds must be really good on our cars.
Dave

 

In the engine compartment yes - would be horribly hot and there is nowhere near enough room for the stock battery.

However my fender mount gel battery stays much cooler than the stock battery inside the box - where it gets heat soaked from the engine & exhaust heat under the car

Alan

 

Just fit a trickle charge connector somewhere (mine is under the rear license plate), and keep it as full as it can be. Parallel charging is difficult to manage - special eqt required to do it properly.
jp 83 Euro S AT 53k.