Hey guys. My car is finally running like a dream. I mean, it's idling perfectly, I can use my A/C and it just won't overheat even in the worst traffic but as usual, things could not stay this way for a long time. My battery decided to let me know it's about to call it a day. Voltage is dropping and the other day I had to refill the water.

I notice that with the extra load of the new fans and the A/C working all the time the voltage is dropping to low numbers (in the 11 volts range when I'm driving at night).

So, here's my question: can I buy one with more capacity? Would there be any downside to doing so?

Thanks

 

I've got an optima battery, only downside is the weight, and you have to modify the battery tie down a bit to get one to fit.
Oh and they are somewhat pricey..

 

My current battery won't fit in the spot where the factory one came. Is your optima battery rated higher than regular ones?

I don't know how you guys measure the batteries there but here; my current one is a 9/12 and what I'm asking is whether I could put in a 11/12 without any issues?

Thanks

 

I'm pretty sure this is the one I have in my car, not positive, I'll have to go look after work.

Optima Red Top 34R-1050 Battery

 

I just put in an Optima 34/78 in my NB and it fits just fine. It is about the same height as the stock battery but has about twice the CCA. You can still use the stock battery clamp with some minor modifications.

No downside that I can think of, other than the cost. Optimas are not cheap but shop around.

 

Ok.

Thanks guys.

 

Here's a pic of mine, model number 75-25 all I had to change was the top metal piece, I made it from one of those brackets you use in a pegboard. I used some rubber sheets with some "greatstuff" sandwiched between it to keep it from sliding around



Not the prettiest thing out there, but who cares?

Here are some specs on the battery:

• 910 Cranking Amps
• 720 Cold Cranking Amps
• 90 Minute Reserve
• 44 AH
• 9.4" Length x 6.8" Width x 7.6" Heigth
• Approx. 33 lbs.
• Notes: Non-Deep Cycle Battery, Standard Auto Posts On Top with GM Side Terminals, Comes with Carrying Strap, Excellent Starting Battery for Cars and Trucks
• Factory Warranty: 36 Months

 

You should not be using a water-fill battery. If you get the correct type battery in there and it still drops while driving, look into your alternator's health.

 

Bruce, I assume you mean a battery that's sealed; right?

And about the alternator; I don't think that's the issue in my case. I think it has to do with the electrical wiring job they did locally while placing the different sensors.

Local electricians just suck.

Nicasus; thanks for the info and pics

 

thread jacklins and resurrectionals!

ZX, that 34/78 is bigger than the D35 right? Looking for one of those for my NB and wanted to see how you got the bigger one to fit.

 

Also in for bigger battery to fit NB for V8 Powah.

 

Rafa, you need an upgraded alternator. The battery does not power the car with the engine on.

 

ideally not, but a deep cycle battery is designed to do just that.

 

BTW, I plan to upgrade the alternator to a 130 amp unit from a Taurus. Fits the 5.0 well. It will carry the bigger electric fans and stuff. I'm more worried about cranking a slightly increased compression 306.

 

Ben, I just changed the battery 1 day ago. I think you're right about needing an upgraded alternator

Any suggestions?

 

I was just about to say the same thing...

Actually, I'm not so sure that your alternator needs to be upgraded, simply repaired. A stock Miata alternator, in good condition, ought to be able to produce >13v with all of the stock accessories running. Yes, I know you've got some aftermarket fans, but they shouldn't be drawing the system down to 11v.

In every town, there is one old man who has been rebuilding starters and alternators since WWII. He has a small shop in an older neighborhood with a hand-painted sign. Find this man, and see if he can restore your alternator to health.

 

Oh, Rafa you have an NA don't you? NA alternators are very low output, though automatics have greater output alts than manuals. The FD RX7 alternator should also bolt up and be an upgrade.

Or do what Joe advises, which is to get the original rebuilt and rewound. There are people who do that; I've had it done on old GM cars multiple times.

 

Sorry just saw this. The 34/78 literally dropped right in. I just had to bend the top bracket a bit to get it to work but it was easy really and obvious what to do. IIRC the issue with the stock clamp was the L-channel looking piece that wraps over the edge of the stock battery. It does not fit the Ultima. So I either bent it flat or removed it completely, I forget which.

+1 on what Joe said though. If you have voltage problems while cruising then it is an alternator issue, unless your battery is really screwed up and pulling power somehow, but I doubt it.

 

my issue is sitting time.

when the battery was new, the car could sit two weeks and start.
now it sits one day and wont start in cold weather.

 

rafa what is your idle RPM?
Alternators will need >1000 rpm to generate full otuput.