I apologize for the lengthy post. I’m hoping it’s a good read though, if you’re interested in a lithium battery for your Evora.
I bought my 2017 Evora 400 last summer. The OEM battery is a getting a bit long in the tooth for a lead acid battery, depending on its care. As folks on the forum know, the Evora has a good amount of parasitic draw which can discharge the battery to low voltage levels in a few weeks’ time. If the battery is allowed to discharge to a certain point, it can end up with sulfation, shortening the lifespan of the battery. Sulfation occurs when sulfur in the solution leaches from the electrolyte and begins to stick to the lead plates becoming lead sulfate crystals. The crystal build up on the lead plates keeps the plates from working as intended and eliminates the needed sulfur in the electrolyte solution. I’m the second owner of my Evora and I don’t know how the battery was cared for. The car didn’t come with the OEM Battery Tender. The original owner must have kept or lost it, so I’ve been using a battery maintainer I already have. I haven’t had any trouble with the battery so far. With COVID going on, all I’ve done are day drives and I immediately put the battery maintainer on when I get back. Now that corona virus vaccines are rolling out, I’m hoping to take a road trip late this summer to visit friends a couple of states away. I would hate then to find out the battery needs replacing in some small town which probably won’t have any group 91/T6 batteries available.
I’ve been checking out the newer LiFePO4 lithium batteries they now make for cars, which are much more expensive. On the bright side though they’re much lighter (lighter makes you go faster everywhere) and have an expected lifespan of 8–10 years. Skip ahead if you’ve read this before, LiFePO4 is a Lithium Iron Phosphate battery (also called lithium ferrophosphate). They’re the safest type of lithium battery as they will not overheat, and even if punctured they will not catch on fire. Due to the oxygen being bonded tightly to the molecule, there is no danger of the battery erupting into flames like there is with LiCoO2 and Lithium Polymer batteries. There’s always tradeoffs though. LiFePO4 doesn’t have the energy density that LiCoO2 does, but LiCoO2 and Lithium polymer batteries lifespan are only about 3 years or so; as many cell phones can attest to.
A lead acid starter battery Ah rating is not as it would appear. A LiFePO4 battery can use 95% of its storage capability (measured as Amp-Hour, Ah), while a lead-acid battery, for starting applications, typically only uses 30%; per Peukert’s Law (it’s a EE thing, if you’re curious). Additionally, LiFePO4 batteries have a flat discharge curve, so their cranking power does not drop-off. What all this means is a LiFePO4 battery that is 1/3 the Ah rating of a lead acid battery, is actually equivalent.
Some Lotus owners on the forum have been using 15Ah and 20 Ah LiFePO4 batteries intended for motorcycles with success; weighing in near 5 lbs (like the ATX-20-HD, ATX20-HD Lithium Motorsports Battery – Antigravity Batteries
). It required modification/removal of the battery tray and different battery cable connectors, although there are car terminal adaptors available (Car Terminal Adapters (SAE) – Antigravity Batteries
). This is great for a track focused car, but not the path I was wanting to take. I found Antigravity Batteries makes a LiFePO4 battery in the Evora’s T6 size. Their T6 comes in 40Ah 1500 CA and 60Ah 1800 CA configurations; same sized battery box. I purchased their 60 Ah 1800 CA T6 battery. It’s not close to 5 lbs, but it is 20 lbs lighter than the lead acid OEM battery it replaced.
LifePO4 batteries have battery management system circuitry (or BMS) in the battery box. The BMS prevents over discharging, over charging and short circuit protections. It has cell balancing as well as thermal protections. This is supposed to extend the lifespan of the battery. The intriguing thing that Antigravity has done with their BMS in this T6 battery is to keep the battery from fully discharging. When the power level reaches a certain point, the BMS switches the battery off. There’s no voltage at the terminals. There’s a button on the battery that when pushed will turn the battery on again. That’s problematic for the Evora, because we can’t easily open the rear hatch to access the battery without power. Fortunately the Antigravity battery comes with two wireless remote control key fobs. When pressed the fob will also turn the battery on. Once the battery is turned on again, there’s enough power left in it to allow you to start the car. They called this feature Re-Start Technology or built-in jump starting. I really like the idea of not being stranded with a dead battery because I left the lights on. LiFePO4 batteries do require a battery charger/maintainer specifically designed for LiFePO4 batteries. I got the CTEK Lithium US Smart Charger 4.3A (P/N 56-926), CTEK Lithium US Smart Charger – Antigravity Batteries
When my Antigravity Battery arrived I found they threw in one of their Battery Trackers, which is a great piece of tech.
I wrote about their Battery Tracker a while ago in this post: Battery Tracker
I don’t use my Evora as a daily driver, because I’m worried about getting door dings, scratches, and nicks that my G35 accrues as my daily driver. People in parking lots, don’t get me started on that subject. Because a LiFePO4 battery is able to dig deeper into its power reserves than a lead acid battery, I’m thinking I shouldn’t need to use a battery maintainer on my Evora until the long winter hibernation. No more cords to connect and trip over. Just jump in and go for a drive. Come winter I’ll just tape the cord to the floor to avoid tripping. As this year progresses, I’ll be watching the battery’s state with my Battery Tracker’s phone app to confirm whether this expectation holds true.