This could be related to a number of things.
1. Dying battery - These do wear out over time, but should take a while to stop accepting a charge. A multi-meter is your friend in this case. A fully charged battery ego depending on the manufacturer will be somewhere between 3.3 volts and 4.2 volts. If your battery is fresh off the charger and is only metering at 2.8 volts (example) there is most likely a problem with the battery and it'll need to be replaced.
2. Worn coil(s) - These coils, even with maintenance, don't last forever. Gunk builds up on them and in the wicks. I don't recommend dry burning many types of coils. Protank or similar bottom coil clearomizers do not have resistance- no resistance coil set ups. The resistance wire is what gets hot. When you dry burn you do run the risk of burning or scorching any rubber insulators that are there. That'll create a nasty burnt taste. This is not the case for every type of clearomizer out there but it is something to be aware of. Dry burning does not always make your coil like new again either. Especially in clearmizers. I have found that sometimes it actually makes things worse. When you dry burn it it can just cause the juice that is inside the portion of the wick that is in the coil to basically turn into a hardened mass effectively blocking off the juice flow to the center of the coil. Resulting in weak and/or dry hits.
PG/VG content - As mentioned earlier the PG/VG ratio could be the culprit. Thicker juices (heavy vg) do not wick as easily.
Dirty Contacts- If the various contact points are dirty it can cause you to have a poor connection and cause weak hits. Make sure both the male and female connections are clean. Check the threads on both (ground) and check the center pins (live). Give them a little cleaning.
Lastly, before you go buying another battery, go hang out at a vape shop for a little bit. Ask them if you can use one of their ego style batteries for a little trouble shooting. It can help you to narrow down the problem. Screw your atomizer onto their battery and see if it is performing the same, then screw their atomizer onto your battery and see. Always better to have your problem narrowed down before you start throwing money at it.
Or, just buy more gear. You wouldn't be the first or the last vaper to buy gear even though you might not need it
Hope your vaping gets better soon!