View attachment 498687 BLUF: In my early 2013 RWD Tesla Model S, I just replaced the Tesla-installed DCS 12V battery with the Lithium version from Ohmmu. In spite of what their website states, this is not a simple “drop-in replacement.” The replacement battery does NOT fit as a simple “drop-in replacement” due to a different spacing between the negative terminal center and the side of the battery case. I am providing this information as a service to others who may be considering purchase of this battery.
DETAILS: My April 2013 RWD Tesla S received a 12v battery alert in early December, informing me that the 12V battery needed to be replaced “soon.” My first 12V battery lasted about 3 years, and was replaced in mid 2016 by Tesla under warranty, at no cost to me. The replacement battery lasted about another 3 years – I received the recent 12V battery replacement alert in late December 2019. Mileage: 62,000 miles.
Using the Tesla app, I scheduled an appointment to replace the battery. Tesla scheduled a mobile appointment for mid January. Several days later, I received an update from Tesla informing me that no 12V batteries were available, and my appointment was now rescheduled to late January, after new batteries were expected to arrive. Given my recent (and many) interactions with Tesla service for both my Tesla vehicles, I became concerned about their ability (and reliability) to meet this new re-scheduled date. I understand that a 12V battery alert doesn’t mean the battery will fail within a few days; but there are no guarantees (or hard data that I’m aware of) that indicates when the battery might completely fail. I did not want my spouse to be stuck somewhere away from home if the 12V battery failed.
I had read much about the Lithium variant offered by Ohmmu. They offered a battery that was clearly advertised on their website as a “drop-in replacement” for the Tesla Model S. Based upon those assurances, I purchased a battery with the idea of replacing it myself. Granted, I was aware of the extremely tight area in which the battery was installed – I had seen it myself when a mobile ranger came to my home to replace the charge port and opened up the frunk trim in order to disconnect the HVIL. I knew I was in for an extremely challenging remove-and-replace event.
After removing the old battery (with lots of grunting, straining, and use of language which my mother would not approve), I installed (i.e. shoehorned) the Ohmmu battery in place. After installing the battery hold down bracket, and the breakout fuse panel on top of the battery, I discovered that the negative battery cable lug did NOT line up with the negative terminal on the new battery. No amount of coaxing, adjusting, prying, or cussing worked. I tried adjusting everything I could think of. Finally I decided to re-measure ALL the battery dimensions. To my surprise, I discovered a difference in the distance between the negative battery terminal bolt hole and the side of the battery case. In the old battery, the distance was 0.75 inches. In the replacement Ohmmu battery, it was 1 inch. This means the negative battery cable must move “inward” by 0.25 inch in order to be connected to the battery terminal bolt hole. That may not sound like much, but it resulted in interference between the battery cable terminal and the breakout fuse panel cover. I contacted Ohmmu by email; they responded immediately suggesting I rotate the battery cable lug. I had already tried that, but I tried again with no success. Finally, I resorted to modifying the breakout fuse panel cover by trimming. I was careful to ensure that no terminals or electrical connectors were exposed. Still; this should not have been required. I informed Ohmmu of what I had to do in order to make this work; their response was: /quote: “Sorry for the inconvenience, each vehicle year/model has some subtle nuances and we try to do our best to support all instances but there are outliers.”/ Interestingly, their web site quotes glowing reviews; however, I did not find a means to post a direct review.
I’ve attached photos to help illustrate.
I was able to make this new battery fit. I feel the website description as a “drop-in replacement” was misleading at best. I can only hope that their description of performance and reliability are indeed accurate.
For those of you with older Tesla Model S, I suggest you keep this in mind if you are thinking of taking on the replacement of the 12V battery yourself.
View attachment 498686