I think having a trickle charger and using it at least monthly if the car is a weekender, is paramount toward maintaining battery health. If the car is a DD then you can treat it normally and yes... Make sure you "lock" the car and shut off ( sleep ) the ECU. My Turbo's have eaten batteries like no other cars I have owned, and that's too many to count over 50++ years. My other 5 or 6 analog 911's never ate volts like these cars do.

 

Thanks all. Started the car today after 5+ days at rest and it started really strong. Guess g the battery was bad after all.
I normally maintain the car on trickle and will continue to do so with the new battery.

 

congrats on the electrical success. It’s not enjoyable driving then parking only to wonder if it will start again.

Simple trickle charger good for FLA (flooded lead acid), but not best for AGM or VRLA. These batteries need a Bulk, roll off, and float AGM pattern from a smart charger.

I routinely get 10-12 years from AGM batteries.

 

So with an agm battery, don’t use a trickle charger? How do o maintain them in the winter?

 

I’ve been using a CTek trickle with AGM setting for many years on several AGM batteries. Never a problem.

 

Almost all trickle chargers sold today are compatible with AGM batteries. AGM batteries are not rare nor special anymore.

 

CTek is a modern charger with AGM profile. As @Carlo_C said, AGM batteries are not special anymore, so most modern battery maintainers or charges have a selectable or automatic AGM profile. The charger or documentation will always state whether or not it has charging profiles.

Old or inexpensive chargers will likely be fixed voltage, whether high (fast) or low (trickle). These chargers can slowly boil out the acid. If you use an old style charger you monitor the battery voltage; after brief bulk charge (up to 14.5V) the battery will accept current in the 13.1-13.75V range but eventually you want the battery long-term at approx 13.1V. When disconnected from the charger it should hold 12.5 to 12.8V. When disconnected after a charging, a newer battery will hold approx 12.75V, older battery will be happy to hold 12.5V. So, the point is you can use a cheap charger as long as you monitor voltage and don't let it burn your battery.

Winter: AGM batteries are usually charged to a Float state (e.g.13.1V) then disconnected from charger (in marine and commercial settings we lift the + and - from the battery completely). Depending on the coldness of winter the battery voltage is checked in a month and possibly Floated again, but in my experience healthy AGMs can last 3 months of a New England winter without maintenance charge before recommissioning charge.

There are advanced chargers which include a Recondition profile; this is a good thing to try if you're at the point of replacing a battery as it will recover at least some if not a lot of charge cycles. Some types of AGM (carbon foam AGM) require a Recondition run at specified numbers of cycles.

Of course, this is a lot of hassle for a battery in a Hobby-Summer car. Many owners are fine with letting the battery go whenever, then order another one installed. I am a bit **** about battery life because I was responsible for banks of 1,000 AmpHours and more. We wanted max life, not only to save money on purchase but also because batteries are heavy and usually located in a remote spot for lifting. A big 8D battery is 200lbs of lead and acid, ready to strain your back or be dropped on a toe.

So you can understand my insanity to get 12 years or more from a battery. Your mileage may vary.

 

All this special charger stuff is overblown.

If special charging is required how come the same alternators/regulators are used with AGM/Flooded batteries?

AGMs are not special anymore. Almost any charger works great.

 

A lot of good info. Thanks all.
I usually just keep the car on the “Porsche”cigarette lighter charger when I’m not driving it. Is that ok, or not needed?

Interesting comment on the marine battery. I’m in WI and every fall I pull the battery and put it my garage. Usually just throw it on a shelf till spring with out issue.
Last year I used a new battery tender/charger and kept it on it all winter. Come spring, battery would not hold a charge. I wonder if I boiled it?

 

I use the NOCO tender and it has a setting for AGM. I permanently installed the pigtail connection right under the battery cables on the posts, and it has a quick connect when I get home - super easy and efficient.

 

it's likely the battery was slowly destroyed by continuous charge.

All batteries are built with a finite number of Charge Cycles possible and an Operating Profile, just like engines or motors have maximum life and an operation procedure to realize those maximums.
Brief relative description of types (high end batteries will include documentation with specifics of operating procedure):

good old Lead Acid: low energy storage capacity/ mass, low charge current acceptance, high current discharge for short periods. Poor ability for long term discharge
Charge acceptance and voltage developed is very temperature sensitive.
Any Depth of Discharge greater than 40% down (or 60% amp-hours remaining) will seriously reduce the number of lifetime charge cycles. If used to give a large discharge it needs to be recharged soon. Cheapest to build, but fragile if dropped, leaks acid if tipped, boils easily. The perfect low-cost small-form-factor battery for simple cars and small motors as a starter. Can use cheap simple alternator/ regulator. FLA is not a fussy or sophisticated device nor is it super reliable, like when it's unable to start your car in a cold winter or dies because your kid left the dome light burning overnight.

AGM types: very good energy storage capacity/ mass, high charge current acceptance, good discharge current but not as high as FLA for comparative battery. Excellent ability for long term discharge.
Charge acceptance and voltage developed less temperature sensitive.
Any Discharge greater than 50% of Amp hour capacity will seriously reduce cycles. Can withstand short periods of being discharged but likes to be pushed back to 100% capacity sooner than later.
Expensive to build but more resistant to shock, can be tilted or oriented any direction, won't boil dangerously. Requires a larger charge source than FLA and a smart regulator to enable the 3-stage charge profile the device requires. With a battery or battery bank of good capacity, the AGM can run your car dome light all night no problem, or run all the lights and appliances on your yacht for the night so you don't run a noisy generator. But the longer AGMs sit discharged the more the life cycles are shortened.

Lithium types: super high storage/mass, super high charge acceptance, super high discharge currents at high or low rates.
Can be discharged to almost zero % capacity without damage - hence a yacht which required 2,000 amp hours AGM or FLA (giving only 1,000 Ah overnight) could use a lithium battery bank half the size, reducing weight and space.
You can leave lithium types 100% or 1% charged, they don't care and will charge right up again. But very fussy for charge profile and management, a complicated expensive energy system Everyone is familiar with the dangers of these batteries with "runaway" if operated improperly. Very expensive, justifiable only for extreme uses (offshore yacht, aircraft, medical equipment, off-grid whole-house etc)

Any of these batteries will work somewhat for any situation, but will work best and economically for the designed use-case.
The hassle of charging and maintaining batteries must be balanced again cost of owner effort/ technician cost.

Any battery charger can be used, but sophisticated chargers require less operator intervention. Very sophisticated chargers are user-programmable - this includes regulators on automotive or marine alternators. A battery bank with multiple charge sources (solar, wind, hydro, regen, genset, drive engine) needs a regulator with multiple charge profiles.

Any charger which is connected to battery long-term must be able to sense the charge state of the battery and then STOP voltage or current impression lest it overheat the battery. Good chargers will stop completely at design threshold, then periodically check the battery voltage. Depending on the charge profile, the charger will turn on when a lower threshold is reached then completely stop charging at the proper upper threshold.

unfortunately a lot of "smart" chargers or trickle chargers do not actually stop impressing voltage on the battery. hence the charger ruined your boat battery over the winter.
sorry to hear.

And again - people run boats and cars all the time without knowing any of the above. the hassle of battery management may not be worth your time, just get a new battery at the dealer every couple of years

 

Thanks, yeah I’m thinking I ruined the boat battery, while that stinks, at least I now know what caused it to be short lived. Won’t make that $200 mistake again.

 

Carlo, you are correct that engine mfgrs continue to supply simple small-case alternators with simple internal regulators, even for cars with large AGM batteries and big electrical loads.

There’s always a big business in marine and RV world upgrading the simple stock alternators/ regulators that come with OEM engines. Even high-end marine turbo diesels (Yanmar, Volvo, Cummins, etc) still supply a simple 1960s style alternator designed to briefly re-charge a small FLA battery. But these small capacity batteries cannot run all the devices on a modern car nor support the “house” loads of a self-contained boat or RV dwelling. So electrical techs get lots of aftermarket business.

Some modern cars and trucks are properly equipped. I have 2020 Escalade. Its 6.2L engine has a large alternator with smart regulator to handle the large AGM battery. I can even run an internal inverter for 110VAC loads from the truck. No external charger needed.

996 and later Porsches have many more devices than the air-cooled cars before them. So, Porsche replaced the old FLA battery with AGM battery to handle the many loads. But I suspect they didn’t replace the old alternator with an upgraded alternator/regulator after my experience with my current 996. The test: my almost new Porsche OEM 80Ah AGM Austrian battery was charged to hold 12.65V. I then drove 1 hour of 65mph highway (to Lime Rock Park raceway). While driving I watched the voltmeter hit 14V then roll off to mid 13V as I would expect. Drove home a solid hour of highway with same voltmeter action.

2 hours of full voltage alternator should easily recharge a battery that started out at 100% – but the battery was down by 30% capacity and holding only 12.1V. Either the alternator is too small for the driving loads, or alternator overheats, or the regulator is dumb and shuts off the charging due to the high load.

Why would Porsche engineers create such an unworkable device? Maybe to hit a price point, or save weight, or there was very limited engine bay space.

Rather than redesign the fanbelt and bracket to hold a large alternator with an extra fan, rather than find space for an external regulator, rather than adding the weight and expense of these upgrades the Porsche engineers kept the old small alternator and advises us to supply an external charger to make up for the inadequacy.

This might be the best alternative. I mean, which would you rather have: 1. engine bay space and weight dedicated to power – or – 2. more weight to run creature comforts and gadgets?

I want horsepower and torque. yay Porsche.

If you don’t externally charge, the AGM will die early from chronic storage in a depleted state. If you use wrong charger the battery will die early by slow boil. Or you can 10x your battery life following mfgr guidelines, saving money, environment, and backaches.