miscrms wrote:Have any Leaf owners tried switching to a good quality deep cycle AGM type battery? I went to an Optima Yellowtop on my 2005 Prius, which is also notorious for undercharging 12V batteries, and have had no issues for 5 yrs. Even in Phoenix, which also tends to also be tough on 12V battery life.
It does seem surprising to me that the Leaf uses a flooded type battery, as well as a conservative charging routine. The only advantage of a 12V flooded I can think of is its tolerance to more aggressive charging. I guess the explanation is in the "reduces the electric power consumption from the Li-ion battery" statement, seems like they went a bit too far in the efficiency direction.
The Leaf does also use a 12V backup capacitor bank as someone else mentioned the Prius does. So its a little surprising that it could still get into this sagging voltage failure mode if that is indeed the cause. Unless I guess the 12V voltage is just not sufficient to charge the cap bank sufficiently? But that voltage should come up quickly as soon as the DC/DC converter engages when going ready? There are DTCs in the brake system and VCM for low 12V voltage, but they don't seem to trip until 10V or so.
Still it doesn't seem like a total brake failure should be possible even if the electronic control system fails completely. According to the manuals (and my own experimentation) there is still manual hydraulic braking force available in the event of a complete system failure. In my case this was simulated by disconnecting all control and power connections to both the ABS and IBU/master cylinder. Without the boost pump I will say the braking is very heavy, and the pedal position quite low from what I recall. So if the brake boost motor cuts out it may well feel like you've lost the brakes, but a firm pressure on the pedal should still stop the car.
Additionally its perhaps worth noting that the parking brake can (according to the manuals) be used while the vehicle is in motion to apply mechanical cable driven force to the rear brakes as long as the handle is pulled up. Of course this motor does depends on 12V power, but not sure how sensitive it is to voltage.
I have used red top Optima batteries in my gasoline engine vehicles in Phoenix for many years and they always last longer than conventional batteries (unless the charging system overcharges them). I purchased a yellow top Optima deep cycle battery for the 2011 Leaf when the original flooded-cell Nissan battery failed even though I could have gotten a replacement from Nissan under warranty. It would be in the 2015 if the insurance company's storage yard would have let me remove it after the 2011 was declared a total loss. I believe the Leaf's charging algorithm is ideal for the yellow top Optima and I will replace the original Nissan battery as soon as it gets weak.
I have also tested the brakes without assist on both the 2011 and 2015 and found that the hydraulic brakes still function, but they require a lot of pedal pressure and the pedal is only about 1/2-inch above the floor. To someone who has not tried this it could seem like the pedal was going to the floor without applying the brakes.