Not to be confused with the 350 volt EV pack
Like all other vehicles on the road (gas, hybrid and EV) electric vehicles like the 2020 Kia Niro EV still incorporate a 12-volt battery (wet battery), despite having a high-voltage battery pack for propulsion. This seemingly traditional component serves several crucial functions in modern EVs. The 12-volt battery powers the vehicle’s auxiliary systems, including lights, infotainment, door locks, and critical electronics such as control units and the electronic parking brake. It also plays a vital role in starting the vehicle by activating the motor controller relay, which allows power to flow from the high-voltage battery to the electric drive motor. Additionally, the 12-volt battery acts as a buffer for the main high-voltage battery pack, smoothing out fluctuations in its output and ensuring a steady supply of electricity to the vehicle’s electrical systems. Without this 12-volt battery, an EV would be unable to start or operate its essential auxiliary functions, even if the main high-voltage battery is fully charged.
Once or twice when returning from a multi-day flight, having left the car at the airport, I found the 12-volt battery had become discharged below an operational level. Normally a “12-volt Wet Battery” has about 13.8 volts at it’s terminals. When it’s down to 11 volts it’s in trouble. When it’s down to 10 volts it is effectively ruined. After this experience on a few fateful mornings I tried to depart for work as usual and the car started but the battery warning lamp was illuminated. I put a voltage meter across it and measured a measly 11.3 volt so I turned off the car and attached the traditional battery trickle charger. This happened more and more frequently as the traditional 12v ‘wet battery’ was failing. Also when a ‘wet battery’ has been depleted below 50% of it’s charge it’s days are numbered. A ‘wet lead-acid’ lifespan is drastically reduced when discharged.
There are different battery technologies for the 12-volt car battery.
- One is the “Wet” battery which is the lead battery with water sloshing around inside (pure, holy water not tap water). These are the least expensive but not very durable. They have a cap that allows venting because while charging the water can essentially boil which releases small amounts of hydrogen (explosive), but the caps attempt to force the vapor to condensate and drip back into the battery (decades ago we had to frequently check the water and add some). Some does escape however as you will notice from the wet appearance around the large caps. Once in a while one should pry off the caps and check the water level. In my experience if you see the tops of lead fins sticking out of the water, exposed, it’s lifetime is about to end. You can add distilled water but just start looking for sales and figuring out what store has the replacement on the shelf.
- Another is the AGM battery. AGM means Absorbed Glass Mat. This type of battery is a modern variant of lead-acid batteries, where the electrolyte is absorbed into fiberglass mats instead of having water sloshing around.
- These are non-spillable and maintenance-free
- Superior power delivery
- Better charging/discharge cycling performance
- Increased vibration and heat/freeze resistance
- Longer lifespan, up to twice that of a wet or ‘flooded’ battery
- The original battery is a “54459”, 400 CCA, SAE(A). Weight 27.4 lbs. 44 AH capacity.
- It has the posts inset with plastic around them that has holes for the battery caps to plug into and the hold-downs are mounted on the sides, not over the top.
- The original also has Calcium laced alloys to provide minimal water loss and very little gassing. Apparently this is what is meant by CMF. “CMF batteries ensure high-performance and minimize reduction of electrolytic solution and self-discharge by using calcium based metal mixture and super-polymer low resistance separators”
- The original battery is ONLY available at the dealership’s parts store and they have to order it! It was also about the price of the AGM!
AGMs are more expensive, but worth the investment. So when my Kia’s original 12 volt flooded battery was failing I shopped for an AGM.
This battery must have the Negative Terminal on the left (if your facing the side with the terminals).
The battery is a DIN “Group H4” size. Advance Auto Parts has a Diehard EV Battery H4 Group, 570 CCA, 80-minute reserve capacity that is an AGM battery.
Original battery Rocket CMF45L-DIN
New AGM battery from DieHard – perfect fit!
Note: I am writing this page a year after replacing the battery. It’s been in the car through the worst summer and winter and still doing great.