I have a laptop that requires about 18.5vdc for the power plug and I also have some batteries that output almost exactly that voltage +/- .2 vdc (topped off the battery voltage is closer to about 19.5-20v but drops to the 18.5 after a minute or two of use).

I would like to be able to use the batteries for the laptop if necessary so I was wondering if there would be any problem with adding a pigtail tap on to the dc connector wire where I can connect the battery to power the laptop.

Is there any reason that this wouldn't work or is there anything that should be taken into account before trying this?

I have tried powering the laptop with higher and lower voltage power supplies and it will run within a range of voltages, down to about 17v or so. Amperage shouldn't be a problem as I know the batteries supply more than enough amperage for the application.

Any suggestions before I try this?

 

adding a pigtail tap on to the dc connector wire where I can connect the battery

Presumably you intended using a plug and socket connection from the battery to the pigtail? If so, wouldn't it be simpler just to wire the battery to a plug which fits the laptop power socket, thus avoiding the need for a pigtail?

 

I was wondering if there would be any problem with adding a pigtail tap on to the dc connector wire where I can connect the battery to power the laptop.

As I understand your question there should be no difficulty provided:

1) Electrical paralleling of the PSU and external battery is rendered impossible (as, for instance, via connection ('oring') by low V(f) rectifiers).

2) Some method of monitoring remaining (external battery) 'run time' is implemented...

3) You are absolutely certain the (described) single supply constitutes the sole power requirement...

Please be aware that 'charge maintenance' of the internal battery will represent a significant fraction of the external battery's load...

Best regards
HP

 

Presumably you intended using a plug and socket connection from the battery to the pigtail? If so, wouldn't it be simpler just to wire the battery to a plug which fits the laptop power socket, thus avoiding the need for a pigtail?

yes if I had a plug of the same size, currently I only have one.