Installing Duracell AGM Batteries

[grizzfan]

My 1973 911T has a two battery set up that has worked well for 5 or 6 years with Interstate batteries designed for the 911. But Montana Winters have extracted their toll on them and one was dead the other limping.

So I went with two Duracell AGM batteries that I ordered from Batteries Plus. (15% off until the end of October 2019 brought the cost to just over $200, no sales tax in MT.)

These were batteries designed for a 2005 Mazda Miata that I heard would fit. Mazda batteries are just too hard to get, even at the dealer and more expensive to boot.

The Duracells are smaller on two dimensions but about 1/2" too tall. That would short them out in the stock battery boxes. So I researched and they can be laid on their side, terminals protruding into the frunk. Did that but the driver's side positive cable is now way too long and try as I might I could not bend it properly to fit.

So I have an appointment at an auto-electric shop in a week to shorten the cables associated with the positive one.

Incidentally, the battery on the passenger side was sufficient to start the engine right up. I'll let you know if I run into anything else.

Tom

[Trackrash]

Those dual battery setups were for extra weight in the front, and originally had something like 300 cranking amps each.

I found an Interstate battery with 600 cranking amps which fit, although it had side terminals, which is actually easy to adapt. I have only used one battery for the past 30 years with no issues. (since moved to the smuggler's box)

I have heard that the AGM batteries can have problems with our old style charging circuits. So let us know how your set up works out.

[grizzfan]

There does not appear to be any weight savings as there fellows weigh every bit as much as the lead-acid ones!!

I did notice that I was pulling 14.6 volts at higher rpms with the Interstates and with only one Duracell AGM in I'm still pulling that much. This is a new occurrence this year. Don't know what that could be.

Tom

[Trackrash]

Yes, that was the problem some have been having. Ruins the battery. I'm not sure what the solution is. My '71 with the stock alternator and a new solid state regulator is 13.7 volts with a conventional battery.

It was suggested that the old style regulator could be adjusted to get the voltage under 14.

[87maniac]

Installed AGM in my VW Westfalia camper.

According to several internet sources, AGM charge voltage is higher than flooded lead/acid.

I installed a adjustable volt. regulator to increase the charging voltage from 13.3V to 14.7V

If this is incorrect, please chime in!

[dicklague]

Originally Posted by grizzfan

My 1973 911T has a two battery set up that has worked well for 5 or 6 years with Interstate batteries designed for the 911. But Montana Winters have extracted their toll on them and one was dead the other limping.

So I went with two Duracell AGM batteries that I ordered from Batteries Plus. (15% off until the end of October 2019 brought the cost to just over $200, no sales tax in MT.)

These were batteries designed for a 2005 Mazda Miata that I heard would fit. Mazda batteries are just too hard to get, even at the dealer and more expensive to boot.

The Duracells are smaller on two dimensions but about 1/2" too tall. That would short them out in the stock battery boxes. So I researched and they can be laid on their side, terminals protruding into the frunk. Did that but the driver's side positive cable is now way too long and try as I might I could not bend it properly to fit.

So I have an appointment at an auto-electric shop in a week to shorten the cables associated with the positive one.

Incidentally, the battery on the passenger side was sufficient to start the engine right up. I'll let you know if I run into anything else.

Tom

I beg to differ with you, but the Miata AGM batteries are not hard to get at all. I have been using them in my 1973 911 for 20 years and just installed the third set.

Batteries Plus was about 30% more expensive than the batteries I ordered on Amazon and had them delivered from NJ in 4 days. They were beautifully packed and shipped USPS Priority mail.

These batteries fit the battery boxes, but you do have to be careful with the positive terminals. I have installed plastic insulating shields to prevent contact above the + terminals.

I will take some photos in the next day or so and post them. I also have newer technology battery terminals that have a clear insulating cover so the + terminal is insulated at the top.

I know the two batteries are for weight and balance and I do want to preserve that. My car weighs 2170 lbs. and I want to keep that weight up front in those corners.

[speedo]

I am in the mkt for a replacement battery for my 72 (only want to run one) and I think I want to run an AGM battery with the front terminals. The Miata batteries each have 320 CCA, but as I only want to run one, what is my minimum required CCA for my 2.4 ltr engine?