Prius C (aqua in Japan) showing check engine / hybrid warning sign

Dear all,
Good to become part of this friendly community. I have researched well from this site before I bought Prius C 2013 having 54k Kms mileage on it. Now in 2 years I drove it to 138k.
Since last 2 weeks I am getting check engine light 3 separate nights.....2 times hybrid system failure warning light and once 5-6times heat warning light blinked and few secs latter check engine pops up. All 3 times I drove to my mechanic and lights were gone by the time they started to diagnose it.
Now what 2-3 mechanics said to me is same that your battery is dead etc.....where as my mileage is same as 2 yrs ago in fact just got throttle body serviced and it improved 10-15% per litre. Btw I always have AC at 22-24 and AC fan at 2-3 bar.
1- Now what I read on different forums is that dead battery will decrease mileage....not happening in my case.
2- battery will drain itsself or unusual drop of bars.....not in my case all is smooth.
3- if the fault is genuinely in the hybrid battery shouldn't be check light staying rather than resetting itself 3 times .....
This light always comes up at late night can moisture cause malfunctioning or confused error by ECU?
In my city due to monsoon rain roads have huge bumps and holes which give car huge jerk even if I cross it 4-6km speed. Also I feel my shocks are weak bearing its 2013 and now it's 2019. Hybrid and engine both coolant need to be replaced which I will do tomorrow.
Is it possible that due to hybrid coolant or bumps mak it's computer system malfunction and pops error??? Also can computer ECU get it's grips loose due to bumps and humps? Or can it get carbon by any chance?
Hybrid cooling fan is cleaned regularly and is perfect....
A friend of mine said to get hybrid battery serviced saying its points get carbon and cause current to flow poorly and unevenly. Do u guys recommend it?
need help guys as I am thinking to sell it rather than burn 1000$ on the used battery.
Also has anyone faced dead hybrid battery ??? If so how it started acting up and what was the behaviour ? And how old Ur car is? Mileage? Suggestions?
Kindly help.

 

Thanks for comforting me about the battery.
Finally light came during the day n took it to workshop scanned and it's rear O2 sensor ....will check both O2 and replace.

 

Yes u r right mate, used Toyota equipment for diagnosis and it showed rear O2 sensor. So will check both O2 and replace the faulty one. Appreciate Ur help mate.

 

Ok I replaced O2 sensor rear one as per the codes system showed , replaced all coolants, got battery fan serviced, hybrid battery pack serviced. But after 2 hour 30min on trial run normal city drive it again popped check engine light.....I knew this light comes after car heats up so I kept car on for such long time. Now this car with exclamation also popped up tonite.....this is 3rd time it has popped up in 2 weeks or so.
When I start in morning it will b gone only check engine and by the time I reach my technician check engine also goes away.
Need serious help guys.....I will replaced front O2 sensor too...air mass sensor also working fine so is water pump etc. Throttle body serviced , tuning done , new engine oil + filter + air filter....all genuine.
Here I must add 2 times in past weeks on rash driving my heat warning sign blinked 4-6 times I slowed down slightly turned AC high and it never blinked again. This is y I changed all coolants as I have done 138k Kms. I m owning it since last 83k Kms never had any issue.
Also battery response and average is normal.

 

Ok , light again showed with new error code engine coolant pump.....I replaced it and since then 4 days trial and no error any more....
All smiles again.
Thanks for guidance .

 

Is there a way to clear system memory codes the other way???