Bill 993

I'm replacing my 6-year old Interstate MTP91 battery and seeking advice on buying a new AGM type.

The MTP91 fits very well, and has the vent hose in the correct location. Having a vent tube is important since traditional lead-acid battery do vent gas. Interstate's website lists the Mega-Tron Plus 48/H6 as the correct replacement battery (I guess MTP91 is out of production). Does anyone have a 48/H6 and can tell me if the vent tube option is on this battery?

I did a search of old threads and learned the following;
- Most 993 owners are happy with AGM batteries
- One thread mention that the alternator voltage at the battery is on the low side (V = RI loss due to length of cable from engine to front battery location?) and that AGM batteries prefer high charge voltages. Is this a concern?
- AGM batteries don't vent gas (only have emergency over pressure valve) so ok to mount w/o vent tube.

I want to keep everything "stock", so want a battery that drops-in, no mods to bracket or cable. Any recommendations on AGM battery that will just fit?

Thanks for any feedback.

M. Schneider

I've purchased two Interstate brand Mega-Tron + 48/H6 AGM model batteries in the past 6 months. Both were sourced through the N. Georgia area Interstate Battery distributor. One for the 993 coupe and the second battery for a daily driver VW MkV Jetta 1.9 PD diesel.

FYI: Our MY05 Subi Outback XT wagon is left garaged (CO) for months/quarters at a time and its fitted with a 4+ year old AGM type battery .... Recently going strong all summer long.....

As stated, with the AGM type batteries there isn't a traditional battery vent arrangement . . .

jennifer911

Bill, AGM batteries are pretty common now, sourcing one is easy. I just keyed in 1996 993 on a web site called Batteries and Bulbs (it’s some random franchise with 8 stores in the Seattle area). I know nothing about this outfit, but they list a Duracell Platinum AGM battery, group size 48/H6 style battery (Porsche size and shape) for $199 and a 10% off coupon you can use for it. The picture clearly shows the vent hole in the appropriate location for a 911.

AGM batteries are spill proof so they have a valve in the vent mechanism. If the battery overheats or is grossly overcharged etc. the valve opens to off-gas. Other than that they are truly maintenance free. Every type of vehicle battery will have some type of emergency vent (it may be hidden under a decal)

We upgraded our 997.2 battery to an oversized H8 AGM battery recently (we gave the fairly new regular battery to our friend, funny story) and it came with vent holes on both ends. There was a push-in barb for the vent hose and a plug for the other side. Quite universal, no problem to properly mount in the car.

JDB1

Autozone has an excellent battery and it fit perfectly in my '97.

MM993

I have had the new version MTP-H6 in my car since 2014 with no issues. I moved the vent hose from old battery to the new one. Here's a pic. of the hose location on new battery.

eeterp

Batteries Plus carries an AGM and non-AGM replacement. Link: https://www.batteriesplus.com/batter...finder-box-top

NC TRACKRAT

DURACELL AGM H6 is made by East Penn/DEKA and sold at WAL-MART.

Analog Theory

i just replaced mine with The Intererstste MTP91-T6 which was their recommendation as direct replacement (same dimensions). Fit perfectly.

sacman

I had the interstate MTP91-T6 and when it was dead, I brought it back to the local Interstate Dealer for warranty no question asked. I could upgrade to the AGM type but decided not to because the warranty on the AGM is much shorter than that of the MTP91-T6. What I like about interstate is that their exchange program is very simple and easy. They go by the engraved ID on the casing to determine the coverage regardless of where and whose it was purchased.

Bill 993

Thanks for the feedback and comments. I found this article useful to explain the differences in AGM battery types - http://www.hendonpub.com/law_and_ord...ery_technology

Appears to me that the Bosch S6585B S6, DieHard EP-48, Exide FP-AGML3/48, and others all the same case, about the same price (<$200) and are listed as Calcium-Lead AGM types.

The Odyssey and Northstar are be highest price (>$200) group 48 batteries, and are pure-lead plates. Appears that the Interstate MT7 48/H6 could be a re-branded Odyssey, case looks the same and price is ~same as Odyssey purchase directly.

IXLR8

The stock Voltage Regulator is set at 14.5V but at the battery the most I have measured with my on-board voltmeter is 14.2V. A bit low even for a regular flooded lead acid battery.

You are better off slightly undercharging a battery than overcharging it (causing it to gas) and that is especially true of any VRLA battery, AGM and GEL.

Until the Voltage Regulator fails. I'd never mount an un-vented battery in an enclosed space.

centerpunch

Just bought bosch agm at pep boys, $200 with 30% off promo, so $140.

4 year free replacement guarantee.

(Edit, brain fart, corrected source from autozone to pep boys)

tj90

I bought the bosch AGM group 48 battery from pep boys and found that it is too high to fit in the 993 space. The plastic trunk trim is interfering with the top of the battery. I measured 7 3/4" inches from bottom to top and the old autozone battery is 7". The bosch agm batteries now have a black top (they used to be blue). I wonder if it wasnt just a color change but a different top. This battery was mfg 10/2016. Anyone else having this issue?

ronnie993tt

I don't know how close you are to the border but a bunch of us use the Canadian Tire battery specified for our cars. Around $160 Canadian on sale so pocket change in US currency. I've used them in both cars for years and they're good for at least 7 years.