Q: Unable to update 10.11.5       Download stops at about 100MB download!

Repair the Drive for El Capitan

1. Restart the computer and after the chime hold down the Command and R keys until the Utility Menu appears.
2. Select Disk Utility and press the Continue button.
3. Then select the indented (usually, Macintosh HD) volume entry from the the side list.
4. Click on the First Aid tab in the toolbar and wait for the Done button to activate. Click on it, then quit Disk Utility.
5. Select Restart from the Apple menu.

[Permission to use part or all of the above has been granted by Kappy, exclusively, to theratter.]

Resetting your Mac's PRAM and NVRAM

Intel-based Macs: Resetting the System Management Controller (SMC)

Boot the computer using Safe Mode then restart normally. This will be slower than a normal reboot, so be patient.

Download OS X El Capitan 10.11.5 Combo Update and install it.