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Seeking Advice on Noco Genius 5 Charger Overcharging Issue with Lithium Battery:
I installed a Noco Genius 5 charger/maintainer in early December 2024. I had no issues until recently when my 992's BMS activated on two occasions within several weeks. I presumed the first time that BMS activated due to battery depletion. I thought perhaps the maintainer was ineffective due to a loose lead, however, I verified they were both secure. The maintainer was also correctly set to "lithium" mode, so I chalked it up to a fluke. I jumped the car for a drive and reattached the maintainer upon returning.
A few weeks passed before I attempted to unlock the car--only to find it was unresponsive again, so I began troubleshooting. I found the maintainer, while still blinking red, had charged the lithium battery above 15v. I replicated the overcharging on an AGM battery in my other vehicle. The issue persists whether using the lead attachment method, or clamps from battery + to grounding post. Finally, I purchased a second Genius 5 which correctly enters maintaining mode and flashes green when the battery is charged. This applies to both vehicles.
To my surprise, the BMS wasn't activated by a battery depletion--rather, the BMS activated due to battery over-charging. I’ve reviewed this thread but haven’t found anyone reporting a similar issue despite numerous grounding methods and various chargers. Was I unlucky to receive a faulty Noco Genius 5, are my leads improperly installed, or is there something I may have overlooked?
Connecting live and negative or live and ground will charge the battery. Connecting to an insufficient ground will not fry the battery. It simply won’t charge it. What you describe sounds like a faulty maintainer
Trickle Charger Setup
One of my Battery Tender brand chargers recently stopped working, so I picked up a couple CTEK Lithium US chargers as a replacement for two of my Li-ion battery equipped Porsches (you could use a CTEK MXS 5.0 if you have an AGM battery). While revisiting my setup, I decided to switch from SAE to CTEK’s more convenient “Comfort” connector. I also wanted to keep SAE compatibility for instances when my mechanic or dealer needs to put the car on a tender.
Testing Ground Points
Previously, I had the negative eyelet connected directly to the negative battery terminal, but the setup was stretched and inconvenient. To find a better location, I tested several potential ground points using a multimeter set to 200 ohms (negative lead to battery negative post, and positive lead to ground test location). Here’s what I found:
Strut Tower Brace Bolts & 10mm Bolt Near the Strut Tower: Both registered Open Loop (not grounded properly for this use).
10mm Bolt at the Front of the Battery Tie-Down: Registered ~0.02 ohms, the same as the factory ground terminal.
Based on these results, I chose the 10mm bolt at the front of the battery tie-down as my ground point. It’s as good as the factory ground terminal and much more accessible. I recommend this location if you’re not using the negative battery post itself.
New Setup for CTEK & SAE Compatibility
To ensure I could use both the CTEK Comfort connector and SAE for flexibility, I did the following:
Installed an M8 Eyelet to SAE (24-inch) cable and routed it to the location shown in the attached photo.
Connected the CTEK Comfort Indicator Pigtail Adapter to the SAE cable and reinstalled the plastic panels for a clean finish.
If a shop, dealer, or garage needs to use SAE, I can easily remove the CTEK Comfort adapter and leave the SAE connector accessible. For additional compatibility, I also have an SAE to Female Cigarette Adapter for Porsche Charge-o-mat Pro compatibility as well.
M6 would also work though if you locate an alternative in the appropriate length with a fuse.
I also test fit the CTEK Comfort Connect Indicator M6 Eyelet (56-629) and it fit, but just barely. The flange hex nut on the positive battery terminal and 10mm bolt at the front of the battery tie-down both overlapped with the fitting and require bending the eyelet when tightening down. This cable is the right length if you want to skip SAE, but the M8 eyelet size is actually a better fit for both of these flange hex nuts.
thanks for the reply.. when I tried to losen the firewall nut.. I got sparks from the black cable already installed there..
Sorry I missed WHERE you were thinking to attached your negative Maintainer lead. While the main negative lead from the Battery to the Firewall (Chassis) will obviously work, I'm not sure I would disconnect and reconnect that joint with the maintainer lead, as it might compromise that important connection. If you look at all the pictures posted on this thread, there are many other locations that will work, that do not compromise that main negative connections between Battery & Chassis. Your choice, yet I would not use that location.
thanks for the reply.. when I tried to losen the firewall nut.. I got sparks from the black cable already installed there..
That is a vehicle ground loosen that will give you sparks. The “proper” ground is on the drivers side…just far enough away that most cables won’t stretch to the ground and the positive post on the battery…
That is a vehicle ground loosen that will give you sparks. The “proper” ground is on the drivers side…just far enough away that most cables won’t stretch to the ground and the positive post on the battery…
I lengthened my pigtail cable by splicing in a short length of wire. The spliced in cable is of the same AWG as the pigtail cable, joints are soldered and covered in heat shrink plastic of appropriate colour. Makes the pigtail installation neat and effective, terminations at correct locations.
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