Battery saving mode

You can't, if your showing that warning then something is wrong in the electrical system, weak battery, low alternator output(seen bad ECM's do this) bad alternator, corroded wiring. Get the codes pulled and see if those tell you where to head for diagnostics, if there are no codes then live data scanning is the next step.

Probably forgot to hook up an engine ground strap. Jim

I doubt that this problem has anything to do with the lifter/rocker replacement... You just have a bad battery or failing alternator, or the cable connections are faulty. For some reason, the battery isn't getting charged properly or it's not holding charge. The low voltage is also why the remote start won't work. Just have the charging system tested.