Battery Low

That's normal for a non-plugin Prius. In auto/Eco mode, the ECU will go as far as it can in EV mode, before firing the ICE. Try to force the car back into EV mode won't work; the ECU is protecting the battery pack from getting damaged and too low. Once the battery reaches 1/4 to the halfway point, it'll allow you to switch back to EV mode.

Hope this helps....

 

Unless there's been a drastic change for 5th gen, I'd reserve EV for driveway shuffles and the like. With our 3rd gen even that's not possible with a stone-cold engine, unless I spoof it with at least an hour of block heater plugged in. That's something I've taken to doing, say I want to move the car (with cold engine) from garage to driveway/street.

 

That is just the way it works in some driving conditions, especially when lots of low speed ICE-off conditions are encountered, such as low speed city or residential streets. These drain the battery without much ICE-on time to refill it. If they continue long enough, the ICE will be forced on.

Steady flat highway speed conditions are usually very good for getting the charge back up to 'normal'.

Putting the car into EV mode is generally not an effective way to improve MPG, other than in certain conditions such as parking lot movements when the engine is cold and your movement will be short enough that the ICE won't be needed, so EV can be used to avoid an engine warmup cycle.

 

if you want ev mode, trade for a prime

 

i was trying to be helpful. putting your prius in ev mode costs mpg's and reduces the life of the battery to some extent.
take it as you will, no offense intended

 

The amount of charge in the HEV battery will greatly vary as the car switches the ICE on and off. If you were already at the bottom charge level, then the EV mode won't be available.

This is what I like about the Prius Prime—you will always have the EV mode available as long as you keep an eye on the state of charge. I find the EV mode very useful for short trips. I only use the HEV mode for long trips over fifteen miles. If you deplete the EV reservation and reach the bottom of the HEV reservation in the Prius Prime battery, then it becomes a regular Prius, and you may have the same "EV mode not available" blues. It actually displays the exact same message when that is the case and press the EV/HEV button.

 

You stated that you tried putting in EV mode, got the warning, then asked how to get the charge of the battery up.Thinking you want EV mode from that isn't much of a leap.

Earlier generations didn't display reasons for why it didn't go into EV when asked; it simply didn't. The manual had a list of possible causes. It also explained the purpose of EV mode was for parking spot shuffling, and to avoid disturbing neighbors with engine noise. The gen1 and gen2 for the first few years cause Toyota was likely worried people would misuse it, and they didn't want to field complaints about it.

As for your first question about the charge, don't worry about it. The system program will charge the battery up in a manner as efficiently as possible without outside input. Toyota has a lot of experience in keeping hybrid batteries in good shape.