If the laptop doesn't do the onsite job required, you will have just spent money on very expensive doorstop. My experience of Libra & OpenOffice 3rd party 'compatible' office suites is they might load and layout basic files. For complex stuff, multiple files / overlays etc, forget it, they won't do the job.
The Google suggestion will not be compatible with your bespoke application and are cloud based, no onsite mobile data signal, no datasheet to fill in. With a Win 10 / on disc Office 2016 setup you can load the application and save the data with no data link to send when you have a signal.
As the laptop is being moved around alot the most common cause of failure is likely to be g-shocks to the HDD, so I would personally go for an SSD.
The alternative is to repair your current laptop which sounds like a broken charger lead or loose power socket connection. Both are common (Mrs Rods2 an expert on creating both by sitting with laptop on the lap and then walking off with it in her hands with the PSU brick pulled along ) and are easily repaired. If the former check the PSU lead and socket and replace or get a local independent to repair.
Everything else as per TB's suggestions.
Well crikey what a can of worms I have opened up here!!!!!
Many thanks to all who have contributed to the discussion
Rods you are quite correct we have had multiple occasions while using Libre where the document has been scrambled on the receiving end so generally stick to Word, but using Win 10 and saved to one drive, if it all goes tits up on site ,its generally recoverable when back at home.
HOWEVER!!!
Having had a play with the said machine, I decided to take it to bits!! uh oh!!
So battery out , back off, play carefully with power socket , not really knowing what I'm doing so give up , put it all back together and...… it works!!!
Charge light came on powered up no problems , let the kids loose with it all weekend so three or four charge cycles and it now seems fine so will just hold fire a little while to see if it keeps going.
Watch this space and thanks again for all your input everyone