Not according to Battery Tender's "Battery Charging Basics & Charging Algorithm Fundamentals" PDF - page 11.

 

I go through the trunck and have no problem fully closing the lid

 

What voltage does your Battery Tender switch at when going from Bulk to Absorbtion. What voltage does it Float at? And if it temperature compensates, what does it adjust the voltage to? What type of battery is it used on?

I couldn't believe the answer I got from Battery Tender..."publishing the specific voltages corresponding to any timeframe usually just generates more confusion than any resulting benefit". Let me be the judge of that. The main reason why I never took BT too seriously and do not own one.

 

Just pull one of the rubber drain plugs on the bottom of the trunk pan and run the wire up through to the battery.

 

Hmm. Interesting. Is it possible the pdf is out of date? Here are excerpts from the manual that came with them. The third paragraph is where I got the information I posted. I interpreted it to mean both chargers are 3-stage units, but I can see how the wording might only cleverly imply that. At any rate, these chargers have worked flawlessly for me and countless others for many years.

 

FWIW (and that may be not very much): On my 993 (and previously on my SC) I placed a heavy gauge wire from the battery thru the firewall and under the carpet to a tender in the foot well behind/under the driver's seat. I have a coiled AC cord that I simply pull thru the driver's window to a nearby outlet. When I get in the car I just pull it out of the outlet and it drop it in the foot well behind the set. This has been servicing my cars for 25 years with zero problems. Easy to see the green light with the seat back forward. I'd hate to screw around with the cord coming into or out of the front. Plus, I'd hate to be opening and closing the hood regularly just to get the charge. Further, this process keeps the garage "clean" of stuff and cords laying around. --- Just one guy's approach.

 

Dave, there is only one way to find out.

Measure the voltage as it is increasing during the constant current aka bulk mode and once it reaches a peak at about 14.2 to 14.4V, see if it switches instantly to a float mode in the mid 13 V range.

If after the bulk mode it stays in a constant voltage mode for a few hours before switching to float mode, then it is a 3-stage charger.

Yes, I read that a lot. I read comments like "my battery has lasted 3 years and I use a BT". Well I would hope it lasted that...3 years isn't what I call a long battery life. Ten-plus years...now we are starting to talk long battery life. How about 13 and still going and 18 year battery life.

Any battery charger is better than no battery charger if a battery would normally be neglected. As for battery chargers and how well they charge, there is a world of difference.

BTW, that PDF is right from their present-day web site.

 

me too...been doing this for 10 years...no issues.

 

I just run the cord out the front of the trunk and close the trunk. No harm to the seal. Have been doing this for almost 20 years on 2 911s and the 993 with no issues. (The 997 goes out the back of the front lid.)

I do tie a flag on the drop down extension cord to prevent driving away without unplugging it in my haste to get on the road.