DD716TED wrote:
I know that the onboard power panel is only a maintainer not a charger.. ..
I doubt that is true at all.
Most likely that the batteries will charge up just fine when the power is restored but it might take several days.
If it will be several MORE days until the power comes back on, you should disconnect the batteries until then. Operating a battery disconnect switch, if there is one, should do that nicely.
And finally, there is a fair chance that this episode will cause the batteries to age a LOT; such that they might need to be replaced now.